Feldspar SARA IRSL dating of very low dose rate aeolian sediments from Sandwick South,Unst, Shetland |
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| Institution: | 1. SUERC, Scottish Enterprise and Technology Park, Rankine Avenue, East Kilbride, Scotland, G75 0QF, UK;2. Department of Anthropology, Bates College, Pettengill Hall, Lewiston, ME 04240, USA;1. Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden;2. Department of Environmental Sciences, Norwegian University of Life Sciences, PO Box 5003, NO-1432 Ås, Norway;1. Département de Préhistoire du Muséum national d’Histoire naturelle, UMR 7194, 1 rue René-Panhard, 75013 Paris, France;2. Institut de Chimie et des Matériaux Paris-Est, UMR7182 du CNRS, 2 à 8 rue Henri Dunant, 94320 Thiais, France;3. CEA, I²BM, Orsay Cedex 91401, France;4. College of Geography Science, Nanjing Normal University, Nanjing 210023, China;5. UMR 8198 Evo-Eco-Paléo, Université Lille 1, Villeneuve d''Ascq Cedex, F- 59655, France;6. Halma-Ipel, UMR 8164 CNRS, Université de Lille 1, Villeneuve d''Ascq, F-59655, France;1. Luminescence Dating Laboratory, Birbal Sahni Institute of Palaeobotany, Lucknow, 226007, India;2. Department of Humanities and Social Sciences, Indian Institute of Science Education and Research, Mohali, 140306, India;3. Centre for Nuclear Technologies, Risoe-DTU, 4000, Roskilde, Denmark;4. Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India;5. Department of Archaeology and Ancient History, Faculty of Arts, The Maharaja Sayajirao University of Baroda, Vadodara, 390002, India;6. Department of Geology, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara, 390002, India;7. Centre of Advanced Study in Geology, Panjab University, Chandigarh, 160014, India;8. CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad, 500007, India;1. State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS), Nanjing 210008, China;2. MSG Group, Sanya Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China;3. Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences, Lanzhou 730000, China;4. Zhejiang Institute of Hydrogeology and Engineering Geology, Ningbo 315012, China;1. U.S. Geological Survey, Denver Federal Ctr., MS 974, Denver, CO 80225-5046, USA;2. Massachusetts Archeological Society, 50 Village Ave., Dedham, MA 02026, USA;3. New England Antiquities Research Association, 58 Cortland Road, Milford, NH 03055, USA;4. Town of Upton Historical Commission, 14 Plain St, Upton, MA 01568, USA;1. Interdisciplinary Research Institute on Bio-Nano-Science of Babe?-Bolyai University, Treboniu Laurean 42, 400271 Cluj-Napoca, Romania;2. Faculty of Physics, Babe?-Bolyai University, M. Kog?lniceanu 1, 400084 Cluj-Napoca, Romania;3. Chair of Geomorphology, University of Bayreuth, 95440 Bayreuth, Germany;4. Faculty of Environmental Science and Engineering, Babe?-Bolyai University, Fântânele 30, 400294 Cluj-Napoca, Romania;5. Faculty of Humanities, Valahia University, Lt. Stancu Ion 34-36, 130115 Târgovi?te, Romania;6. Institute of Speology, Romanian Academy, 400006 Cluj-Napoca, Romania |
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| Abstract: | Young sediments, with low sensitivity and low dose rates, are challenging for luminescence dating. Here, we present work on the site of Sandwick South, a Norse settlement, in which these challenges were present. Field gamma dose rates below 0.1 mGy a?1, and total dose rates of 0.4–0.5 mGy a?1, combined with expected ages of less than 1 ka, resulted in a requirement for quantitative determination of equivalent doses of 0.2–0.4 Gy. The bedrock geology of the area are metagabbros, which explain both the exceptionally low dose rates and the lack of autochthonous quartz. Luminescence profiling during fieldwork revealed stratigraphically progressive OSL and IRSL signals, indicating phases in the sediments with dating potential. While laboratory characterisation recovered some quartz, its low yields and luminescence sensitivity precluded application of quartz methods. Electron microscopy confirmed the presence of feldspars, which were separated and used for IRSL Single Aliquot Regeneration Additive (SARA) analysis. Counting times for both high resolution gamma spectrometry (HRGS) and thick source beta counting (TSBC) measurements were extended by 1 order of magnitude, resulting in overall uncertainties of <6% for these low dose rates. Dose estimates were obtained using an adapted SARA protocol, incorporating long overnight preheats before first measurement, with the aim of mitigating short-term fading effects. Using these procedures, archaeologically meaningful dates were obtained from this difficult material, which are internally consistent, coherent with stratigraphy, and concordant with the radiocarbon constraints of the associated archaeological settlement. The dates demonstrate sand accumulation in the early to mid-13th century AD and also in the 18th century AD, which are contemporary with disruptive sand movements registered in other coastal regions of the Northeast Atlantic and North Sea regions. The approaches adopted here have provided solutions to the challenging conditions of this young, insensitive material and can therefore be considered to extend the range and applicability of luminescence dating methods. |
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| Keywords: | Feldspar IRSL SARA Low activity Low sensitivity Young sands |
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