Optically Stimulated Luminescence Age Estimates Research Articles

Pleistocene environments, climate, and human activity in Britain during Marine Isotope Stage 7: insights from Oak Tree Fields, Cerney Wick, Gloucestershire

ABSTRACTInvestigations at Oak Tree Fields, Cerney Wick, Gloucestershire, in western England have revealed a sequence of fluvial deposits dating from Marine Oxygen Isotope Stage (MIS) 7 to 5. At the base of the sequence, a series of gravel and sand facies were deposited, initially as part of a meandering river. Reductions in flow energy of the latter and avulsion led to the development of short‐lived channels and episodic backwater environments, the deposits of which are recorded as Facies Associations 1–3. Poorly sorted, probably colluvial deposits formed beyond the limit of the channel (Facies Association 4). Mollusca, Coleoptera, plant macrofossils, pollen and vertebrates recovered from the channel facies indicate broadly similar climatic conditions throughout accretion. Temperature ranges derived from mutual climatic range analysis of the Coleoptera almost completely overlap with those of Cerney Wick at the present day, albeit that winters may have been cooler when the channel was active. Further, the floral and faunal data suggest that the meandering river flowed through an open grassland environment, the latter heavily grazed by large vertebrates, most notably mammoth. Most of the botanical and faunal remains, together with four optically stimulated luminescence (OSL) age estimates ranging from 225 ± 23 to 187 ± 19 ka, suggest correlation of the channel deposits with MIS 7. The basal deposits (Facies Association 1) yielded the majority of vertebrate remains and all the lithic artefacts, most of which seem likely to have travelled only a short distance. Although only a few artefacts were recovered, they add to the relatively limited evidence of human activity from the upper Thames. The channel deposits are overlain by sheet gravels (Facies Association 5) which are attributed to the Northmoor Member of the Upper Thames Formation. These were likely to have been deposited as bedload in a braided stream environment, while two OSL age estimates of 129 ± 14 and 112 ± 11 ka suggest accumulation during MIS 5.

Luminescence and radiocarbon dates from alluvial sediments, Podhale, Central Europe — A methods comparison

Optically stimulated luminescence (OSL) and radiocarbon (14C) techniques were employed to investigate the absolute ages of alluvial sediments in Podhale in the West Carpathians, southern Poland. This is an approach to (i) testing the credibility of the above dating methods by their reciprocal age control and (ii) further implications to regional geochronology and to dating campaigns of alluvial sequences elsewhere. Nine geological sections comprised of mineral and organic material were selected for the study. Our age determinations range from 26.9 to 2.27 ka, and are in good geochronological order. OSL age estimates show good agreement with independent ages from radiocarbon dating. However, in three alluvial successions the discrepancy between the resulting ages is considerable. We attribute the difference to the partial bleaching, and organic material redeposition. We also report on an age reversal of sediments in a single geological section. This might have been resulted from the alluviation-erosion scheme of meandering rivers over a millennial time-scale, i.e. the dominance of channel migration, point bar deposition (lateral accretion), and crosswise erosion. Finally, new geochronological data are provided abolishing sediment age assumptions based on uncertain chronostratigraphical approaches.

Extending the range of optically stimulated luminescence dating using vein-quartz and quartzite sedimentary pebbles

The feasibility of applying optically stimulated luminescence (OSL) techniques to obtain estimates of the burial age of lithic clasts in the form of pebbles of quartzose lithology is investigated in this study. We applied OSL measurement procedures to vein-quartz and quartzite pebbles from contexts at five sites with fluvial and coastal beach contexts of depositional age ranging from 500 ka to the mid Holocene. As in previous OSL studies with lithics, measured depth-dose profiles were interpreted to identify regions associated with key stages in the burial history of the pebbles, including the extent of pre-burial optical resetting, primary burial and any subsequent secondary stages of exposure to sunlight. While some of the pebbles had not been fully optically reset before burial, none were in field saturation, as commonly encountered with larger lithic clasts such as cobbles. The relatively low concentrations of radionuclides within vein-quartz and quartzite pebbles simplified the assessment of the radiation dose rate. OSL age estimates consistent with independent dating evidence were obtained for the three sites sampled in the UK (Langford Quarry, Leet Hill Quarry, Swanscombe Skull Site and Barnfield Pit) and one of two sites tested in Portugal (Forte Cão), whereas evidence of secondary optical bleaching detected in pebbles from a second site (Vale de Atela) underestimated the independent age for primary burial. The oldest depositional age of the contexts tested was ~500 ka (Leet Hill Quarry), and for some of the pebbles tested there was the capacity to extend the potential dating range further as the age equivalence of the limiting value of D e was in excess of 1 Ma. The advantages of working with smaller, portable, clasts in the form of pebbles and with a lithology of higher transparency opens up a wide range of potential applications, whether the depositional processes are environmental or anthropogenic in origin or modification. • New approach to the dating of Quaternary sediments containing vein-quartz and quartzite pebbles. • OSL techniques applied to sliced pebble cores produce depth-dose profiles that are related to optical exposure history. • Successful comparison of OSL ages with independently dated MIS 12, MIS 11, MIS 5 and Holocene depositional contexts. • Low dose rates for vein-quartz and quartzite pebbles potentially enable further extension of the dating range.

Multitechnique dating of earthen irrigation canals at the La Playa site, Sonora, Mexico

AbstractLa Playa (SON:F:10:3) is an archaeological site in Sonora, Mexico that contains the remains of an extensive preceramic earthen irrigation canal system. Modern floodplain erosion has destroyed the majority of these canals, but geoarchaeological investigations on areas of the system that remain reveal much about this early agricultural technology. Comprehensive dating using accelerator mass spectrometry 14C on gastropods, charcoal, and soil humates and single‐grain optically stimulated luminescence (OSL) dating on canal sediments revealed that multiple irrigation systems were used at La Playa during at least two periods during the Early Agricultural period (~750–350 B.C. and ~ A.D. 50–250). 14C and OSL age estimates from canals are in agreement with the earliest direct dates on maize from La Playa (A.D. 20–240), indicating that the introduction of maize corresponds to a significant investment in the modification of the floodplain environment for canal irrigation. The late phase of canal use (~A.D. 50–250) occurs before destructive floodplain erosion at the site. This is contemporaneous with local cultural changes, including the development of a new ceramic tradition, changes in burial practices, and changing subsistence strategies. These results demonstrate the utility of the combined 14C and OSL approach for dating ancient earthen canals.

Chronology of advance and recession dynamics of the southern Green Bay Lobe of the Laurentide Ice Sheet, south-central Wisconsin, USA

AbstractWe used a combination of accelerator mass spectrometry (AMS) radiocarbon dating, optically stimulated luminescence (OSL) age estimates, and stratigraphic data from cores collected along the southern margin of the Green Bay Lobe (GBL) of the Laurentide Ice Sheet to provide new information on the timing and dynamics of the end of advance of the GBL and the dynamics of the ice sheet while very near its maximum position. Coring at multiple sites along the margin of the GBL indicate that ice had reached a stable position near its maximum extent by 24.7 ka; that ice advanced several kilometers to the Marine Isotope Stage 2 maximum position sometime shortly after 21.2 ka; and that ice remained at or beyond that position through the time interval represented by an OSL age estimate of 19.2 ± 3.2 ka. The timeline developed from these chronological data is internally consistent with, and further refines, AMS radiocarbon ages and OSL age estimates previously published for the southern margin of the GBL. It also provides new chronological control on the expansion of the GBL from its late Marine Isotope Stage (MIS) 3 extent to its MIS 2 maximum.

The development of the Princess Charlotte Bay chenier plain: New results and insights

Abstract Chenier plains record changes in the mode of coastal progradation between periods of mudflat accumulation and coarse sediment deposition. The geomorphic development of the Princess Charlotte Bay chenier plain was last considered in the 1980s and the conclusions have contributed to knowledge of muddy coastal morphodynamics. Obtaining new data through the use of luminescence dating techniques provided an opportunity to reassess previous findings. Data were obtained from the south western portion of the bay where the chenier ridges were most distinct whereas previous research had been concentrated on the far eastern periphery of the plain. Optically-stimulated luminescence age estimates and radiocarbon ages from eight of the 11 most seaward chenier ridges yielded a new depositional chronology. The recent chenier sequence in this area began forming with the establishment of the most landward chenier ridge (ridge 1) no more than 4000 yr BP. In the ~ 1500 years following this, two more chenier ridges were built (ridges 2 and 3, which were not sampled). Ridge 4 was being built at around 2400 yr BP, ridges 5 and 6 at around 2100 yr BP, ridge 7 at around 1900 yr BP, ridges 8 and 9 at around 1300 yr BP, ridge 10 (which was not dated) between 1300 and 820 yr BP, and ridge 11 at around 820 cal yr BP. Comparing the new data to previous data and conclusions yielded new insights into the Holocene development of the chenier plain. These new insights may provide a means for Australian chenier plains to inform contemporary coastal morphodynamics more broadly.

Luminescence dating without sand lenses: An application of OSL to coarse-grained alluvial fan deposits of the Lost River Range, Idaho, USA

Optically stimulated luminescence (OSL) dating is increasingly used to estimate the age of fluvial deposits. A significant limitation, however, has been that conventional techniques of sampling and dose rate estimation are suitable only for thick (>60 cm) layers consisting of sand size or finer grains. Application of OSL dating to deposits lacking such layers remains a significant challenge. Alluvial fans along the western front of the Lost River Range in east-central Idaho, USA are one example. Deposits are typically pebble to cobble sheetflood gravels with a sandy matrix but thin to absent sand lenses. As a result, the majority of samples for this project were collected by excavating matrix material from gravelly deposits under light-safe tarps or at night. To examine the contributions of different grain-size fractions to calculated dose-rates, multiple grain-size fractions were analyzed using ICP–MS, high resolution gamma spectrometry and XRF. Dose rates from bulk sediment samples were 0.4–40% (mean of 18%) lower than dose-rate estimates from the sand-size fractions alone, illustrating the importance of representative sampling for dose rate determination. We attribute the difference to the low dose-rate contribution from radio-nuclide poor carbonate pebbles and cobbles that occur disproportionately in clast sizes larger than sand. Where possible, dose rates were based on bulk sediment samples since they integrate the dose-rate contribution from all grain sizes. Equivalent dose distributions showed little evidence for partial bleaching. However, many samples had significant kurtosis and/or overdispersion, possibly due to grain-size related microdosimetry effects, accumulation of pedogenic carbonate or post-depositional sediment mixing. Our OSL age estimates range from 4 to 120 ka, preserve stratigraphic and geomorphic order, and show good agreement with independent ages from tephra correlation and U-series dating of pedogenic carbonate. Furthermore, multiple samples from the same deposit produced ages in good agreement. This study demonstrates that with modified sampling methods and careful consideration of the dose rate, OSL dating can be successfully applied to coarse-grained deposits of climatic and tectonic significance that may be difficult to date by other methods.

The notion of climate-driven strath-terrace production assessed via dissimilar stream-process response to late Quaternary climate

Previous research results from the Gabilan Mesa are combined with new optically stimulated luminescence (OSL) age estimates and sedimentological analyses with the aim of identifying factors that inhibit climate-driven strath-terrace production, and factors that make possible strath-terrace production independent of climate forcing. The factors are revealed by comparing the morphostratigraphy and OSL age estimates of terraces in the adjacent San Lorenzo Creek and Pancho Rico Creek drainage basins of the central California Coast Ranges. OSL age estimates on San Lorenzo Creek fill-terrace alluvium overlying bedrock at two paleofluvial levels range between 50.5 and 41.3ka and between 33.4 and 18.2ka. These OSL age estimates indicate that although the channel of Pancho Rico Creek was degrading at these times, San Lorenzo Creek aggradation was synchronous with previously documented regional, climatically driven aggradation that elsewhere in southern California led to strath production and alluvial deposition. The regional-scale climate forcing events had different effects on San Lorenzo and Pancho Rico Creeks because of the influences of drainage-basin lithology on bedload size and tectonic tilting direction on base-level fall. The Holocene history of channel denudation and strath production of Pancho Rico Creek is also different from that of San Lorenzo Creek, and different from that of many other streams in southern California. After Pancho Rico Creek captured the upper part of the drainage basin of San Lorenzo Creek sometime after 15.5 to 11.7ka, Pancho Rico Creek has been producing unpaired, erosional strath terraces. The weak, clay rich, fine-grained sedimentary rock underlying Pancho Rico Valley is an ideal substrate in which to form straths. The meandering channel of Pancho Rico Creek produces straths, and weathering resistant, relatively hard bedload introduced by stream capture ensures their preservation as strath terraces.

Luminescence chronology of the Grub-Kranawetberg site, Austria

Abstract. Das Alter von acht Proben aus einem Lössprofil der Freilandfundstelle Grub-Kranawetberg (Niederösterreich) wurde mittels der Lumineszenzmethoden der IRSL-Datierungen an der polymineralischen Feinkornfraktion und der OSL-Datierungen an der Mittelkornfraktion von Quarzen bestimmt. Kalibrierte Radiokohlenstoffalter von ca. 30 ka für den archäologischen Hauptfundhorizont AH4 werden innerhalb der Fehlergrenzen durch IRSL- und OSL-Alter bestätigt. Anomales Ausheilen der feldspat-dominierten Feinkornfraktion konnte im Labor nicht nachgewiesen werden, weshalb die MAAD-IRSL Alter nicht korrigiert wurden. Während die meisten IRSL- und OSL-Alter innerhalb ihrer Fehlergrenzen übereinstimmen, unterschätzen einige IRSL-Alter die OSL-Alter aus bisher unbekannten Gründen signifikant, wobei die Mittelwerte der OSL-Resultate tendenziell älter als die IRSLDatierungen sind. Nach den OSL-Altern wurde der aufgeschlossene Löss einschließlich eines interstadialen Bodenkomplexes („Stillfried B“) im Zeitraum zwischen ca. 47 ka und ca. 30 ka gebildet. Mögliche edostratigraphische Korrelationen mit einigen europäischen Lössgebieten sowie paläoökologische Überlegungen zur menschlichen Besiedlung im Jungpaläolithikum werden diskutiert.

Luminescence dating indicates radiocarbon age underestimation in late Pleistocene fluvial deposits from eastern England

Robust geochronological control is crucial for interpreting and correlating the environmental record from fragmentary terrestrial sequences from the last glacial period. Traditional terrestrial stratigraphies are typically reliant on radiocarbon dating, although estimates of antiquity for samples older than 40 ka may be unreliable. Optically stimulated luminescence (OSL) dating of sediments is an alternative for dating the whole of the last glacial period and also provides the opportunity to independently test radiocarbon based chronologies. This paper presents a set of nine directly comparable paired OSL and accelerator mass spectrometry (AMS) radiocarbon ages from multiple sites within Devensian fluvial sediments in lowland Britain and shows that it is possible to obtain robust OSL age estimates throughout this time period. The two techniques agree well for ages younger than ca. 29 14C ka BP (ca. 35 cal. ka BP) but disagree beyond ca. 35 14C ka BP (ca. 40 cal. ka BP). This is thought to be due to radiocarbon ages on older organic material having been contaminated by low levels of modern carbon. It is therefore suggested that all conventionally pre-treated radiocarbon ages greater than 35 14C ka BP should be treated with extreme caution.

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.

Luminescence chronology of Pleistocene marine terraces of Capo Vaticano peninsula (Calabria, Southern Italy)

Quaternary terrace deposits exposed on the Capo Vaticano peninsula (Calabria, Southern Italy) have been investigated in order to obtain new OSL age estimates. Six samples were collected from unconsolidated sediments associated with the major marine terraces. These form a flight of seven distinct levels distributed between about 600 m and 30 m of altitude. The samples were analysed by optically stimulated luminescence (OSL) technique, the obtained results provided reliable age estimates showing numerical ages ranging between 214 ± 25 ka and 62 ± 6 ka. Age determinations combined with geological and morphological information provide new constraints for correlating the distinct orders of marine terraces with the last seven interglacial stages of the eustatic curve. This correlation indicates that in the Middle-Late Pleistocene this portion of the southern Calabrian arc was affected by a vigorous uplift characterized by rates up to ∼2 mm/y.

Late Pleistocene fluvial dynamics in the Hochrhein Valley and in the Upper Rhine Graben: chronological frame

During the Pleistocene, the Rhine glacier system acted as a major south–north erosion and transport medium from the Swiss Alps into the Upper Rhine Graben, which has been the main sediment sink forming low angle debris fans. Only some aggradation resulted in the formation of terraces. Optically stimulated luminescence (OSL) and radiocarbon dating have been applied to set up a more reliable chronological frame of Late Pleistocene and Holocene fluvial activity in the western Hochrhein Valley and in the southern part of the Upper Rhine Graben. The stratigraphically oldest deposits exposed, a braided-river facies, yielded OSL age estimates ranging from 59.6 ± 6.2 to 33.1 ± 3.0 ka. The data set does not enable to distinguish between a linear age increase triggered by a continuous autocyclical aggradation or two (or more) age clusters, for example around 35 ka and around 55 ka, triggered by climate change, including stadial and interstadial periods (sensu Dansgaard–Oeschger cycles). The braided river facies is discontinuously (hiatus) covered by coarse-grained gravel-rich sediments deposited most likely during a single event or short-time period of major melt water discharge postdating the Last Glacial Maximum. OSL age estimates of fluvial and aeolian sediments from the above coarse-grained sediment layer are between 16.4 ± 0.8 and 10.6 ± 0.5 ka, and make a correlation with the Late Glacial period very likely. The youngest fluvial aggradation period correlates to the beginning of the Little Ice Age, as confirmed by OSL and radiocarbon ages.

Timing of Holocene sand accumulation along the coast of central and SE Vietnam

In Vietnam, the coastal sand barriers and dunes located in front of the steep slopes of the high rising Truong Son Mountains are sensitive to climate and environment change and give evidence for Holocene sea-level rise. The outer barrier sands were deposited shortly before or contemporaneous with the local sea-level high stand along the Van Phong Bay postdating the last glacial maximum (LGM). Optically stimulated luminescence (OSL) dating yielded deposition ages ranging from 8.3 ± 0.6 to 6.2 ± 0.3 ka for the stratigraphically oldest exposed barrier sands. Further periods of sand accumulation took place between 2.7 and 2.5 ka and between 0.7 and 0.5 ka. The youngest period of sand mobilisation was dated to 0.2 ± 0.01 ka and is most likely related to reworked sand from mining activities. At the Suoi Tien section in southern central Vietnam, the deposition of the inner barrier sands very likely correlate with an earlier sea-level high stand prior to the last glaciation. OSL age estimates range from 276 ± 17 to 139 ± 15 ka. OSL dating significantly improves our knowledge about the sedimentary dynamics along the coast of Vietnam during the Holocene.

Developments in optically stimulated luminescence age control for geoarchaeological sediments and hearths in western New South Wales, Australia

Research conducted by the Western New South Wales Archaeology Program (WNSWAP) provides the opportunity to assess the reliability of optically stimulated luminescence (OSL) dating of late Pleistocene and Holocene fluvial sediments and burnt stone samples from arid zone geoarchaeological contexts. A large number of radiocarbon age determinations of charcoal preserved in heat retainer hearths provides independent chronological control at these contexts. We describe a rapid OSL methodology for dating burnt hearth stones to complement previously applied radiocarbon methods, which we have tested using 37 samples from hearths with radiocarbon determinations. We propose a geoarchaeological model in which these hearths were constructed by people whose activity took place on an archaeological surface, formed by the earlier deposition of fluvial sediments. Here we demonstrate the veracity of this model by dating sediments lying stratigraphically below the hearths, and use the radiocarbon age control and chronological consistency to assess the accuracy and reliability of both small aliquot and single grain single aliquot regenerative-dose (SAR) OSL dating. While small aliquot age estimates are in most cases in agreement with independent control, the single grain determinations using a finite mixture model (FMM) appear to provide improved chronological resolution. Using single grains, we note some problems in the application of the FMM and in the dating of young samples in the range of 1–100 years. As many samples may have resided close to the surface since deposition, we have developed a mathematical function to describe gamma and cosmic dose rate contributions at burial depths down to 40 cm. These OSL age estimates allow us to reject the model of intensification of human activity as responsible for the observed pattern of archaeological radiocarbon determinations in this part of the Australian arid zone.

Luminescence dating indicates radiocarbon age underestimation in late Pleistocene fluvial deposits from eastern England

AbstractRobust geochronological control is crucial for interpreting and correlating the environmental record from fragmentary terrestrial sequences from the last glacial period. Traditional terrestrial stratigraphies are typically reliant on radiocarbon dating, although estimates of antiquity for samples older than 40 ka may be unreliable. Optically stimulated luminescence (OSL) dating of sediments is an alternative for dating the whole of the last glacial period and also provides the opportunity to independently test radiocarbon based chronologies. This paper presents a set of nine directly comparable paired OSL and accelerator mass spectrometry (AMS) radiocarbon ages from multiple sites within Devensian fluvial sediments in lowland Britain and shows that it is possible to obtain robust OSL age estimates throughout this time period. The two techniques agree well for ages younger than ca. 29 14C ka BP (ca. 35 cal. ka BP) but disagree beyond ca. 35 14C ka BP (ca. 40 cal. ka BP). This is thought to be due to radiocarbon ages on older organic material having been contaminated by low levels of modern carbon. It is therefore suggested that all conventionally pre‐treated radiocarbon ages greater than 35 14C ka BP should be treated with extreme caution. Copyright © 2009 John Wiley & Sons, Ltd.

SEDIMENTARY HISTORY AND THE INTERPRETATION OF LATE QUATERNARY DUNE RECORDS: EXAMPLES FROM THE TIRARI DESERT, AUSTRALIA AND THE KALAHARI, SOUTH ÁFRICA

Stabilized sand deposits from arid regions are often used as palaeoenvironmental proxies for past periods of enhanced aeolian activity. Although widespread use of optically stimulated luminescence (OSL) dating techniques has opened up the possibility of systematic analyses of dune building chronologies, palaeoenvironmental histories cannot be reconstructed from chronological data alone. The reconstruction of regional palaeoenvironmental histories should consider all available evidence - stratigraphic, sedimentological and micromorphological, and chronological. This paper highlights potential issues with the interpretation of dune records in the context of stratigraphic preservation, using examples from the Tirari Desert in Australia and the Kalahari Desert in southern Africa. Sedimentological characterisation of linear dunes in the Tirari Desert demonstrates that reworking of underlying dune sediments and buried soils is common, thereby calling into question simplistic interpretations of dune formation involving sequential deposition and pedogenesis. This case study highlights the limitation of the augering technique, although useful information can be gained nonetheless. Three OSL age estimates confirm the presence of at least two Holocene dune building episodes, but cannot constrain the timing of the onset of dune building. Higher frequency sampling and micromorphological analyses may further elucidate the palaeoenvironmental history of individual dunes. In the Southwestern Kalahari, interdune sediments have been described as the least sensitive part of the aeolian landscape, thus offering the potential for longer records of aeolian deposition. This is found not to be the case at Witpan, where interdune sands are extensively mixed and probably younger than the linear dune cores. The lunette at Witpan records numerous short-lived and rapid deflationary events from the nearby pan (playa). These are considered to reflect changes in sediment source rather than pedogenesis. These examples highlight the value of combining micromorphological, sedimentological and chronological studies for palaeoenvironmental reconstruction.

Age-estimate evidence for Middle-Late Pleistocene aggradation of River Nene 1st Terrace deposits at Whittlesey, eastern England

At Whittlesey, eastern England, Pleistocene interglacial sediments (unit G3) deposited in marine oxygen isotope stage (MIS) 7 appear to be truncated by a sequence comprising: (i) a limestone-rich gravel containing organic mud beds (unit F1); (ii) vertically aggrading gravel beds with sand-clay-lined bases (unit F2); and (iii) interbedded sands and gravels (units F4–F6) with associated overbank deposits (unit G4). Preliminary investigations of the floral and faunal assemblages of the organic muds were consistent in providing evidence for deposition under cool conditions. This apparent single cool/cold-phase sequence therefore could have been deposited in either MIS 6 or MIS 5d−2. The presence of sand beds in units F5, F6 and G4 and of molluscs in the organic mud beds of unit F1 provided the opportunity for obtaining age estimates using optically stimulated luminescence (OSL) and amino acid racemization (AAR). Rather than a single cool/cold-phase sequence the age-estimate data revealed multiphase aggradation, with the AAR data indicating the possibility that the organic muds in unit F1 were deposited earlier in MIS 7 than the interglacial deposits of unit G3. Therefore, the succession could be: unit F1 was truncated initially by unit G3, with unit F2 subsequently incising both unit F1 and unit G3. The OSL age estimates indicate that units F5, F6 and G4 are Early to Middle Devensian in age (MIS 5d-2), and therefore unit F2 was deposited sometime between late MIS 7 and MIS 5d. This paper has demonstrated the utility of using dual age-estimate techniques in dating complex fluvial sequences. Furthermore, the organic mud beds of unit F1 could provide important new information on the complex character of the MIS 7 interglacial. In addition, the OSL data and the fluvial style recorded by units F4–F6 and G4 allow comparisons to be made with recent investigations of nearby Devensian deposits.

Optical dating of hydromagmatic volcanoes on the southwestern coast of Jeju Island, Korea

Jeju Island, the largest Quaternary volcanic island in Korea, has formed mostly since the early Pleistocene, but its latest chronology of volcanism and sedimentation is still poorly constrained. Here we report optically stimulated luminescence (OSL) ages for two hydromagmatic volcanoes on the southwestern coast of Jeju Island, i.e., the Songaksan and Suwolbong tuff rings. The basaltic tuffs of these volcanoes contain abundant quartz sands from underlying marine sedimentary sequences. Two samples collected from the middle part of the Songaksan Tuff yielded highly reproducible quartz single-aliquot regenerative-dose (SAR) OSL ages of 7.0±0.3 ka, providing the first direct age estimate of Holocene volcanism in Jeju Island. The quartz OSL age estimate of 5.1±0.3 ka for the younger reworked basaltic tuff (the Hamori Formation) is comparable with previous radiocarbon and U-series disequilibrium dating of fossil mollusk shells. Two samples from the Suwolbong Tuff show quartz OSL age estimates of 18.3±0.7 and 18.6±0.9 ka, which are identical within error ranges and younger than the quartz OSL age estimate of 23.2±1.0 ka for the underlying Gosan Formation. This study confirms that volcanism and attendant sedimentation were active in Jeju Island until very recently.

Optically stimulated luminescence dating of Southern High Plains archaeological sites

The Southern High Plains of North America is rich in archaeological sites, but many are not well constrained chronologically, owing to a lack of material for radiocarbon dating. A program of optically stimulated luminescence (OSL) dating, applying mainly single-grain analyses, was therefore initiated. Many samples have independent age estimates from radiocarbon to check the OSL results, but OSL age estimates are also provided for those sites that otherwise lack secure chronological control. Sediment samples for OSL were obtained primarily from Paleoindian and Archaic localities, though include deposits of more recent age. Through the analysis of single grains, equivalent dose—the numerator of the age equation—is evaluated independently on numerous grains. The distribution of these values is relatively broad for some samples, and this is attributed to post-depositional mixing. Mixing is also evident in some samples with more narrow distributions. Selecting portions of the mixed distributions for age determination allows more accurate dating for some samples, but the nature of the distributions limits the resolution on others, conclusions that cannot be as easily drawn from multi-grain analysis. Where independent age control is available, most OSL results broadly conform; however, some samples show discrepancies that are not readily explained, but may relate to association or dose rate problems. This underscores the desirability of obtaining where possible suites of chronological evidence.