Advancements and best practices for analysis and correlation of tephra and cryptotephra in ice |
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| Institution: | 1. Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA;2. School of Earth and Climate Sciences, University of Maine, Orono, ME 04469, USA;3. New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA;4. Climate Change Institute, University of Maine, Orono, ME 04460, USA;1. Nuclear Risk Research Center, Central Research Institute of Electric Power Industry, Chiba 270-1194, Japan;2. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8567, Japan;3. Laboratory of Disaster Prevention, National Institute for Rural Engineering, Tsukuba 305-8609, Japan;1. Department of Earth Science, University of Bergen, Allégaten 41, 5007, Bergen, Norway;2. Bjerknes Centre for Climate Research, Bergen, Norway;3. Department of Geography, University of Cambridge, Downing Place, CB2 3EN, Cambridge, United Kingdom;1. Geography and Environment, University of Southampton, Southampton, SO17 1BJ, UK;2. School of Geography, Archaeology and Palaeoecology, Queen''s University Belfast, Belfast, BT7 1NN, UK;3. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada;4. Omagh Minerals Ltd, 56 Botera Upper Rd., Omagh, BT78 5LH, UK;5. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, TX, 78705, USA;1. Department of Archaeology, University of Iceland, Sæmundargötu 10, 101, Reykjavík, Iceland;2. Institute of Geography, School of GeoSciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP, Scotland, UK;1. Department of Geology, Trinity College Dublin, Dublin, Ireland;2. Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford, UK;3. Department of Geological Engineering, Hacettepe University, Ankara, Turkey;4. Instituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli-Osservatorio Vesuviano, Napoli, Italy;5. Department of Earth Sciences, Università degli Studi di Firenze, Firenze, Italy;6. School of Physical and Geographical Sciences, Keele University, Keele, UK;7. Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy;8. Department of Earth Sciences, Royal Holloway University of London, Egham, UK;9. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Naples, Italy;10. Dipartimento di Fisica “E. R. Caianiello”, Università degli Studi di Salerno, Fisciano, SA, Italy;11. Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy |
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| Abstract: | Geochemical analysis of fine grained (<20 μm) tephra found in ice cores is inherently difficult, due to the typically low number and small size of available particles. Ice core tephra samples require specialized sample preparation techniques to maximize the amount of information that can be gained from these logistically limited samples that may provide important chronology to an ice record, as well as linking glacial, marine and terrestrial sediments. We have developed a flexible workflow for preparation of tephra and cryptotephra samples to allow accurate and robust geochemical fingerprinting, which is fundamental to tephrochronology. The samples can be prepared so that secondary electron imagery can be obtained for morphological characterization of the samples to ensure that the sample is tephra-bearing and then the sample can be further prepared for quantitative electron microprobe analysis using wavelength dispersive techniques (EMP-WDS), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), laser ablation inductively coupled mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). Some samples may be too small for typical instrumentation conditions to be used (i.e. 20 μm beam on the EMP) to analyze for geochemistry and we present other techniques that can be employed to obtain accurate, although less precise, geochemistry. Methods include analyzing unpolished tephra shards less than 5 μm in diameter with a 1 μm beam on an SEM; using the “broad beam overlap” EMP method on irregular particles less than 20 μm in diameter, and analyzing microlitic shards as well as aphyric shards using EMP to increase the number of analyzed shards in low abundance tephra layers. The methods presented are flexible enough to be employed in other geological environments (terrestrial, marine and glacial) which will help maximize and integrate multiple environments into the overall tephra framework. |
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| Keywords: | Sample preparation Ice core Microanalysis Glass geochemistry Tephrochronology Cryptotephra |
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