Exploratory Single Grain OSL Analysis of Sediments from Capu di Locu, Corsica

Single grain optically stimulated luminescence (OSL) measurements have been conducted on retained material from sediment samples collected during excavations of Neolithic monuments at Capu di Locu, Belvédère, SW Corsica. One sample was taken from a presumed burial chamber at Tola and two from the lower fill of the construction pit of a menhir at Stantare. Analysis was conducted on 150-250 µm quartz grains previously separated for single aliquot regeneration (SAR) measurements, and on 250-500 µm grains prepared for this analysis. Single grain measurements, including analysis of blank discs prior to dispensing mineral grains, were conducting on a Risø DA-20 automatic reader, with 800-1000 grains measured for each of two samples, and approximately 350 grains for the third sample. These exploratory measurements have demonstrated that a relatively large proportion (>20%) of mineral grains produce significant OSL counts for both the natural stored dose and following a 25 Gy artificial dose. Previous analysis of these samples using multi-grain aliquots measured using a single aliquot regeneration (SAR) protocol had shown broad dose distributions, with mixtures of aliquots of different ages. The single grain measurements have confirmed that these are mixed age deposits. Two samples show stored dose distributions around mean values which correspond to archaeological ages, for the third the stored dose distribution is significantly broader with no apparent archaeological age component. Further statistical analysis of these data would be required to attempt to resolve archaeological age material, that could potentially be used to further constrain construction dates for these monuments. It is expected that similar luminescence properties would be exhibited by mineral grains from other samples collected during the excavations of these sites, and it is possible that further single grain OSL analysis of other parts of the site may produce dose distributions with less mixing and more readily resolved components with archaeological ages. Meanwhile SG apparent ages were obtained from the Tola sample which are consistent with previous estimates, and two new estimates have been achieved from the Stantare site which indicate potential for recovering archaeological ages in the 3rd to 4th millennium BC from the Menhir site

Luminescence dating of wind-blown sands from the Broo Peninsula, Shetland

This report provides a temporal framework to support University of Stirling geo-archaeological investigations near Huesbreck, Broo Pennisula (Shetland), examining how the early modern population there, adapted to harsh climate conditions in the 18-19th centuries, when enhanced aeolian activity led to an influx of sand to the area, leading to adaption’s in farming practices, and abandonment of several sites. Five sediment samples were submitted to the luminescence laboratories at SUERC for dating. All samples were subjected to laboratory preparation of sand-sized quartz, and purity checked using scanning electron microscopy. Dose rates for the bulk sediment were evaluated using analyses of the uranium, thorium and potassium concentrations obtained by high resolution gamma spectrometry coupled with beta dose rate measurement using thick source beta counting, and in situ field gamma spectroscopy. Equivalent doses were determined by OSL from 32 aliquots of quartz per sample using the quartz single-aliquot-regenerative (SAR) procedure. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Radial plotting methods revealed good internal homogeneity in the dose distributions obtained for each sample. The chronology established for the sampled sands on the site spans from the mid 16th century (AD 1540 ± 40; SUTL2441) through to the early 19th century (AD 1810 ± 25), with the dates falling within three clusters - the waning stages of the Little Ice Age, the mid 18th century (AD 1730 ± 25 to 1760 ± 25) and the early 19th century (AD 1810 ± 25). In the wider region, periods of sand movement and deposition in the mid 18th century, and early to late 18th century, are documented in sediment statigraphies sectioned at the Old Scatness Broch, Scatness

OSL investigations at Hardisty, Alberta, Canada: Sections HD03, HD04 & HD05

This report is concerned with optically stimulated luminescence (OSL) investigations of a number of sediment stratigraphies in the Battle River Valley area, near Hardisty, east-central Alberta. Archaeological investigations in this region, led by Rob Wondrasek, have identified thousands of historical artefacts, including projectile points and lithic fragments indicative of occupation. Ken Munyikwa visited the archaeological sites at Hardisty in June 2014 and January 2015 to sample key units within the sediment stratigraphies for OSL dating. The sediments associated with the artefacts were appraised through five profiles, Hardisty-1 (HD01) to Hardisty-5 (HD05), comprised of 43 field-profiling and 14 dating samples. Profiles HD01 and HD02 were sampled in June 2014; and profiles HD03 through to HD05 in January 2015. The dating questions associated with these materials relate to the age of artefact-bearing horizon, through dating the enclosing sediments above and beneath the archaeological soil, it should be possible to provide terminus post quem (TPQ) and terminus ante quem (TAQ) on the age of the artefacts. The conventional quartz SAR OSL approach was examined as a potential method for providing the depositional ages of the sediment enclosing the artefacts. Luminescence profiling during fieldwork had revealed stratigraphically progressive IRSL and OSL signals, indicating sediment with dating potential. Dose rate estimates from these sediments were assessed using a combination of high resolution gamma spectrometry (HRGS) and thick source beta counting (TSBC), reconciled with each other, water contents and modelled micro-dosimetry. Where appropriate, the external gamma dose rates received at the position of the dating sample were reconstructed from the adjacent bulk gamma spectrometry samples, yielding wet gamma dose rates between 0.42 and 0.54 mGy a-1, which are comparable with those recorded at each sampling position. Equivalent doses were determined by OSL from 16-48 aliquots of quartz per sample (depending on quartz yields) using a single-aliquot-regenerative (SAR) approach. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Radial plotting methods revealed some heterogeneity in the equivalent dose distributions of each sample, indicating that each sample enclosed mixed-age materials, reflecting variable bleaching at deposition. The field profiles provide some measure of control on this. Luminescence ages were calculated using standard microdosimetric models, with uncertainties that combined measurement and fitting errors from the SAR analysis, all dose rate evaluation uncertainties, and allowance for the calibration uncertainties of the sources and reference materials. The quartz OSL ages reported here for the sand sequences at HD03 to HD05, contribute to the expanding catalogue of chronological data on the depositional sequences at Hardisty, and further, provide the means to assess the temporal and spatial distribution of artefacts across the site. The sediment chronologies established for each profile are internally and mutually coherent, spanning at HD03 from 7.3 ± 0.3 ka (SUTL2778) to 9.0 ± 0.5 ka (SUTL2780), at HD04 from 7.0 ± 0.3 ka (SUTL2781) to 8.3 ± 0.4 ka (SUTL2782), and at HD05 from 8.3 ± 0.5 ka (SUTL2783) to 9.6 ± 0.6 ka (SUTL2785). The field profile at HD05 reveals some complexity to its depositional history, with notable maxima and inversions in intensities from 150cm depth, potentially reflecting reworking and re-deposition of sediment within this sequence. TAQ for this phase of reworking is provided by the youngest unit examined in the profile, which at 7.5 ± 0.6 ka (SUTL2784), is consistent with the occupational phase recorded in the adjacent sections. The sediment chronologies established in this dating campaign, and in the 2014 campaign, are synchronous suggesting contemporaneous deposition across the site, and presumably, with local knowledge, scope for further age modelling including the use of Bayesian methods to refine the TAQ and TPQ age limits

Luminescence dating of sediments from Underhoull and Lund, Unst, Shetland

This report concerns optically stimulated luminescence (OSL) investigations of sediments from the the foreshore at Burga Sands, Underhoull, and a dune section at Lund, in south-west Unst (Shetland). Samples were collected in February 2016 to establish the timing of sand accumulation, adding to an expanding set of dated sand blows in the Northern Isles and Scotland. The resulting chronologies define the local environmental record of sand movements in the vicinity of Underhoull and Lund, with their adjacent Norse longhouses and chapel. The sediment stratigraphies on the foreshore of Burga Sands were explored through four profiles, comprising the natural accumulations adjacent to two noosts (profiles 1 and 2), and the substrate sequences immediately beneath the noosts (P3&4). The dune section at Lund was explored in a single profile (P5). This report describes the progression from fieldwork and sampling, through initial luminescence screening measurements made with the portable OSL reader (on 45 samples), to subsequent calibrated analysis in the laboratory, first, to characterise the OSL and IRSL signals from each sample, then by targeted quantitative OSL dating on a further set of 10 samples. The ‘field profiles’ provided the first indication that the substrate stratigraphies at Underhoull, extend from the late glacial period to the modern day. The maxima and dynamic ranges in signal intensities for the sequences beneath the noosts, suggest that the construction and modification of these structures were temporally distinct. For the Lund section, the range in signal intensities through these sediments, indicate a shorter chronology, which was confirmed by subsequent characterisation of the profiling samples in the laboratory. The following chronology was obtained for the Underhoull section: 1) onset of sand activity, as recorded in the sedimentary archives of profiles 1 and 2, at 3.22 ± 0.29 ka (1210 ± 290BC; SUTL2861) and 1.99 ± 0.15 ka (AD30 ± 150; SUTL2863) 2) modification and re-build of the first noost at 0.48 ± 0.06 ka (AD1540 ± 60; SUTL2866) 3) construction of the second noost at 0.81 ± 0.07 ka (AD1210 ± 70; SUTL2867) 4) continued sand movements into the early 20th century AD (0.12 ± 0.06 ka; AD1900 ± 60; SUTL2862), with arguably heightened activity at the onset of the Little Ice Age (0.64 ± 0.10 ka; AD 1380 ± 60; SUTL2866). For the Lund dune section, the sediment chronology spans from the early 14th century AD through to the early 18th century AD (0.70 ± 0.05 ka; SUTL2868, through 0.52 ± 0.04 ka; SUTL2869, to 0.31 ± 0.02 ka; SUTL2870), corresponding with the onset and waning stages of the Little Ice Age. The chronology presented here is consistent with an emerging regional framework of sand movements in the Northern Isles and Scotland, with activity in the Neolithic, Early and Late Bronze Ages, the Iron Age, the Viking/Medieval period, and Little Ice Age. The Underhoull section dated here provides a broad chronology for sand blow and, importantly, places sediments underneath two noosts into the late Norse/ Mediaeval period. The dune section dates a high resolution local record within the last 700 years. Opportunities to extend the high resolution palaeoenvironmental record were identified in the adjacent land and dune-scape, and especially in the palaeo-loch landward of the Lund section, which has received sand in the past

Exploratory Single Grain OSL Analysis of Sediments from Capu di Locu, Corsica

Single grain optically stimulated luminescence (OSL) measurements have been conducted on retained material from sediment samples collected during excavations of Neolithic monuments at Capu di Locu, Belvédère, SW Corsica. One sample was taken from a presumed burial chamber at Tola and two from the lower fill of the construction pit of a menhir at Stantare. Analysis was conducted on 150-250 µm quartz grains previously separated for single aliquot regeneration (SAR) measurements, and on 250-500 µm grains prepared for this analysis. Single grain measurements, including analysis of blank discs prior to dispensing mineral grains, were conducting on a Risø DA-20 automatic reader, with 800-1000 grains measured for each of two samples, and approximately 350 grains for the third sample. These exploratory measurements have demonstrated that a relatively large proportion (>20%) of mineral grains produce significant OSL counts for both the natural stored dose and following a 25 Gy artificial dose. Previous analysis of these samples using multi-grain aliquots measured using a single aliquot regeneration (SAR) protocol had shown broad dose distributions, with mixtures of aliquots of different ages. The single grain measurements have confirmed that these are mixed age deposits. Two samples show stored dose distributions around mean values which correspond to archaeological ages, for the third the stored dose distribution is significantly broader with no apparent archaeological age component. Further statistical analysis of these data would be required to attempt to resolve archaeological age material, that could potentially be used to further constrain construction dates for these monuments. It is expected that similar luminescence properties would be exhibited by mineral grains from other samples collected during the excavations of these sites, and it is possible that further single grain OSL analysis of other parts of the site may produce dose distributions with less mixing and more readily resolved components with archaeological ages. Meanwhile SG apparent ages were obtained from the Tola sample which are consistent with previous estimates, and two new estimates have been achieved from the Stantare site which indicate potential for recovering archaeological ages in the 3rd to 4th millennium BC from the Menhir site

Luminescence Dating of Sediments from the Baile Sear Wheelhouse, North Uist

This report provides an Optically Stimulated Luminescence (OSL) chronology for the construction, occupation and abandonment sequence of the Baile Sear Wheelhouse structure in North Uist. The structure was exposed following coastal erosion in 2005, and was excavated by SCAPE with community support in 2009 and 2010. The site was visited by David Sanderson in September 2010 to collect OSL samples. The sediments associated with the monument and its immediate environment were reviewed, and luminescence profiling was undertaken to evaluate the sequence, and to identify sampling positions for OSL dating. Luminescence profiling, using portable field equipment, was used to guide sampling and interpretation. Field gamma spectrometry was used to record the environmental dose rates in the positions of the OSL dating tube samples. Luminescence profiling was undertaken in 7 sections. Profiles 1 and 2 examined substrates below the wheelhouse structure, and an underlying burnt earth surface which represents an earlier structure. The dating questions associated with this material, relate to the age of the earlier structure and the construction of the wheelhouse. Profiles 3 and 4 examined the stratigraphy of sediments immediately outside the southern wheelhouse wall, which record a collapse of the southern wall, and subsequent repacking. The dating questions here relate to the timing of the collapse and repacking events relative to wheelhouse construction and the occupation evidence within the southern chamber. Profile 5 examined the infill of the southern interior area, including materials associated with part of the occupation period and deliberate abandonment of this part of the wheelhouse. The chronology of this abandonment relative to the wall collapse is of interest. Profiles 6 and 7 examined the infill of the central and northern interior areas, including occupation evidence, a hearth sequence, and aeolian sands associated with the final abandonment. In total 58 profiling samples and 11 tube samples with associated field dosimetry were collected, from these 7 profiles, which together represent all of the key phases of activity associated with the construction, use and abandonment of the Baile Sear wheelhouse. The wheelhouse itself is located within a broader sequence of mounds in the vicinity, and which may, together with the other monuments in the surrounding landscape have also contributed to the archaeological materials in proximity to the site. OSL analyses of the profiling samples, both in the field, and in the laboratory have been reported elsewhere. This report concerns the OSL dating measurements conducted using the Single Aliquot Regenerative (SAR) method from 10 of the OSL dating samples, and there use to determine a chronology for the site. Sample preparation and analysis was undertaken at the Scottish Universities Environmental Research Centre (SUERC). OSL SAR dating utilises extracted quartz from the samples to determine the radiation dose experienced by the sediments since their last zeroing event, assumed to be by exposure to light prior to final deposition. This is combined with dose rate analysis based on field and laboratory measurements of environmental radioactivity. The age is determined as the ratio of dose divided by dose rate. In this work, dose rates for the bulk sediment were quantified using high resolution gamma spectrometry and thick source beta counting in the laboratory, coupled with water content analysis and in-situ gamma dose rate measurements. Quartz was extracted using standard laboratory procedures, and purity checked with scanning electron microscopy. Equivalent doses were determined, initially, on 16 aliquots of quartz per sample using the quartz single-aliquot regenerative (SAR) procedure, with additional investigation of further sets of 16 to build statistical power for selected pre-heating groups. Radial plotting methods were used to appraise sample homogeneity, and robust statistics were used, for aliquots satisfying SAR acceptance criteria, to estimate equivalent doses. The quartz OSL SAR age estimates have been assessed relative to the stratigraphy of the wheelhouse, in combination with profiling data using both conventional assimilation methods and also a Bayesian approach. Both approaches lead to similar conclusions concerning the overall chronology of site construction, occupation and abandonment as summarised here. (i) OSL profiling verifies that material associated with the earliest Iron Age occupation of the wheelhouse and preceding structure(s) in the vicinity can be found, outside the wheelhouse, in midden deposits which surround and overlie the surviving structures. This material goes back to approximately 400 BC, and some of it predates the wheelhouse construction. (ii) The preceding burnt surface represents a structure of short-lived duration, which spanned the period first/second century BC to the first century AD. Material associated within this structure and its use may be present in the midden deposits around the wheelhouse. (iii) The most probable period for construction of the wheelhouse is in the first/second century AD. (iv) In the monument, material dating to the earliest occupation of the wheelhouse is preserved in the northern chamber, and its associated pits. OSL profiling indicates that the northern chamber was in use during all period of occupation, from the Iron Age construction of the wheelhouse (c AD 150) through to the first millennium AD abandonment of the site (c AD 900-1000). (v) In the southern chamber, the earliest occupation phases are poorly represented in surviving debris. The collapse of the southern wall (c AD 600-750), the rebuild (c AD 750), the last occupation the southern chamber (c AD 750), and abandonment of the southern chamber (c AD 750) all occur in the later part of the first millennium AD, significantly after the wheelhouse construction and earlier phases of occupation. (vi) After the southern chamber was abandoned, the central and northern chambers remained in use. The central chamber contains a hearth sequence, which indicates occupation of this chamber through a later phase of occupation (~ 700AD) until the Norse period (~ AD 940). OSL profiles provide some evidence of earlier occupation in the central area. (vii) Final abandonment of the site is registered by clean abandonment sands starting from the tenth century AD, consistent with abandonment in the Norse period, and with the upper occupation in the northern and central chambers. Later evidence of aeolian activity through the Little Ice Age (up to 16th century AD) is also recorded in the upper sand fills of the central and northern chambers. The combination of field and laboratory luminescence profiling techniques, and quartz OSL SAR dating, has provided a chronological framework to interpret the complete sequence of construction, occupation and phased abandonment of the wheelhouse structure. To our knowledge, this is the first time that field and laboratory luminescence profiling techniques coupled to quantitative OSL SAR analysis and Bayesian assimilation methods have been applied to define the complete sequence of construction, occupation and abandonment of a site of this type. A further review of other artefact, environmental and dating evidence, would be useful as the rest of the post-excavation work advances

Luminescence dating of wind-blown sands from the Broo Peninsula, Shetland

This report provides a temporal framework to support University of Stirling geo-archaeological investigations near Huesbreck, Broo Pennisula (Shetland), examining how the early modern population there, adapted to harsh climate conditions in the 18-19th centuries, when enhanced aeolian activity led to an influx of sand to the area, leading to adaption’s in farming practices, and abandonment of several sites. Five sediment samples were submitted to the luminescence laboratories at SUERC for dating. All samples were subjected to laboratory preparation of sand-sized quartz, and purity checked using scanning electron microscopy. Dose rates for the bulk sediment were evaluated using analyses of the uranium, thorium and potassium concentrations obtained by high resolution gamma spectrometry coupled with beta dose rate measurement using thick source beta counting, and in situ field gamma spectroscopy. Equivalent doses were determined by OSL from 32 aliquots of quartz per sample using the quartz single-aliquot-regenerative (SAR) procedure. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Radial plotting methods revealed good internal homogeneity in the dose distributions obtained for each sample. The chronology established for the sampled sands on the site spans from the mid 16th century (AD 1540 ± 40; SUTL2441) through to the early 19th century (AD 1810 ± 25), with the dates falling within three clusters - the waning stages of the Little Ice Age, the mid 18th century (AD 1730 ± 25 to 1760 ± 25) and the early 19th century (AD 1810 ± 25). In the wider region, periods of sand movement and deposition in the mid 18th century, and early to late 18th century, are documented in sediment statigraphies sectioned at the Old Scatness Broch, Scatness

Applying luminescence methods to geo-archaeology: a case study from Stronsay, Orkney

ABSTRACTLuminescence methods were used to date a palaeoenvironmental coastal exposure on Stronsay, Orkney. The section consists of glacial sediments that are overlain by intercalated peats and windblown sands, implying varying past environmental conditions. Rapid luminescence characterisation was undertaken using screening methods in combination with quantitative dating of selected samples, providing information on depositional processes and chronology. A temporal discontinuity between the glacial sediments and later peats encompasses the period associated with an important Mesolithic site located inland, and implies erosional episodes. The onset of blanket bog formation on Stronsay dates to 3760±330 yrs BP, consistent with observations elsewhere in Orkney and northern Scotland. Periods of enhanced aeolian activity on Stronsay occurred in the late Bronze Age (2700±265 yrs BP) and at the beginning of the Little Ice Age (650±75 yrs BP). Recent periods of sand deposition in the 19th and 20th centuries (AD 1865±20 and 1960±5) correspond to periods of known historic storminess. These results add to an expanding catalogue of data on sand movements throughout the Holocene in Orkney, and set a framework to interpret the evolution of nearby archaeological and natural landscapes from prehistoric to modern times.</jats:p