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New Results from the "Thera Ashes" Project
Preminoan pumices present a certain difficulty for the identification of Minoan eruption products from excavation sites. Three major eruption cycles produced pumice of a quality similar to that of the Minoan eruption so that we could expect to find these materials in use as abrasive. The events in question are the eruptions of the Lower Pumice 1 and 2 (About 200ka BP), the Middle Pumice (about 100ka BP) and the Cape Riva (about 21ka BP) deposit. Especially the chemical compositions of the Lower Pumices show only minute differences compared to the "Minoan" tephra and the natural range of variation was not know to an extent sufficient for a reliable identification. This has been solved by the preparation of a suitable quantity of material. The element distribution patterns were obtained by instrumental neutron activation analysis (INAA) and the criteria for distinction will be presented. INAA was applied also to determine the stratigraphic distribution of major and trace element abundances within a volcanic ash layer at the archaeological excavation site of Iasos, Turkey. The aim of this project was to determine the content of primary tephra within the 16 cm layer at Iasos produced by the "Minoan eruption" at Santorini. Eight sub-units of the layer were sampled separately and analyzed with different methods including optical microscopy, decarbonatisation and separation of the glassy fraction, and INAA of the vitric particles, the "pure" tephra. The separated fractions were analyzed for the trace element composition to determine any contamination from the overlying soil. These investigations lead to the conclusions that the direct fallout (primary tephra) makes up only the first six centimeters of the layer, whereas the rest are slump portions of tephra, sometimes even mixed with ceramic shards. These findings agree perfectly with the thicknesses of tephra layers reported from lake sediments in Asia Minor. |
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