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Tephra-laboratory

Sample preparation, extraction and identification of tephra

The tephra laboratory at EARTHLAB Chrono is equipped for sample preparation, extraction and identification of tephra from marine, terrestrial and ice core records. The applied quantification method might slightly differ depending on the climate archive, but will follow a roughly similar structure sensu Turney (1998) and Blockley et al. (2005). For example, for marine sediment material the following methodology is applied in order to obtain tephra shard concentrations. A 0.5 g sub-sample of freeze-dried material is diluted with HCl (10%) to remove any carbon matter. The remaining material is wet-sieved into several size fractions ranging from sand-sized shards down to cryptotephra (i.e. >125 µm, 80-125 µm and 25-80 µm) before further separation steps are applied. The latter includes density separation using a heavy liquid flotation technique, dividing the rhyolitic from basaltic tephra shards. To purify the basaltic material it is also possible to perform a magnetic separation at the mineral separation laboratory at the University of Bergen. Hereafter, both microscopic and EPMA slides are prepared on a hot plate by pipetting the separated material onto the appropriate slide covering it with Canada Balsam and Epoxy resin, respectively. Finally, shard concentrations are identified and counted using optical microscopy.

References:

  1. Abbott PM et al., 2011. Identification of cryptotephra horizons in a North East Atlantic marine record spanning marine isotope stages 4 and 5a (60,000-82,000 a b2k). Quaternary International 246, 177-189. 
  2. Abbott PM et al., 2013. Cryptotephrochronology of the Eemian and the Last Interglacial-glacial transition in the North East Atlantic. Journal of Quaternary Science 28: 501-524. 
  3. Blockley SPE et al., 2005. A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. Quaternary Science Reviews 16-17: 1952-1960. 
  4. Davies SM, 2015. Cryptotephras: the revolution in correlation and precision dating. Journal of Quaternary Science 30(2): 114-130.Griggs AJ et al., 2014. Optimising the use of marine tephrochronology in the North Atlantic: a detailed investigation of the Faroe Marine Ash Zones II, III and IV. Quaternary Science Reviews 106: 122-139. 
  5. Haflidason H et al., 2000. The tephrochronology of Iceland and the North Atlantic region during the Middle and Late Quaternary: a review. Journal of Quaternary Science 15: 3-22. 
  6. Lowe DJ, 2011. Tephrochronology and its application: a review. Quaternary Geochronology 6: 107-153. 
  7. Turney CSM, 1998. Extraction of rhyolitic component of Vedde microtephra from minerogenic lake sediments. Journal of Paleolimnology 19: 1999-206.