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.
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