| Summary: | Lake sediment cores from Midge Lake, Livingston Island, South Shetland Islands and Sombre Lake, Signy Island, South Orkney Islands were analysed for volcanic tephra using light microscopy and magnetic susceptibility. Cores were dated using published C-14 and Pb-210 chronologies. Electron probe microanalyses of discrete tephra glass shards were undertaken to characterise the tephra geochemically in order to identify possible source volcanoes and refine tephrochronological data for the region. Results identified five tephra horizons in a core from Midge Lake. Four of these tephra at 3-4 cm, 8-9 cm (c. 450 yr BP), 15-16 cm (c. 755 +/- 1.05 yr BP) and 21-22 cm (c. 1340 +/- 100 yr sp) consisted of sodic basaltic to basaltic-andesitic glasses, containing abundant labradoritic feldspar inclusions, and a single 'acidic' tephra was found at 2-3 cm. Seven tephra horizons were identified in the Sombre Lake core including three basaltic tephra at 3-9 cm (30 +/- 4 yr BP to 125 +/- 25 yr BP), 31-32 cm and 44-46 cm (1325 +/- 50 C-14 yr BP) and four acidic tephra at 21-22 cm and 24-25 cm, 33-36 cm (c. 1021 C-14 yr BP) and 54-56 cm(c. 1450 C-14 yr BP). These are the first tephra to be identified from the South Orkney Islands. Geochemical and grain size analysis indicated that the analysed Midge Lake tephra were derived from the Quaternary Deception Island volcano. Smaller grain sizes, congruent geochemical data and prevailing wind directions also indicate this volcano as the Likely source of Sombre Lake tephra. Results highlight the importance of establishing geochemical consistency between tephra deposited across wide geographical areas, during apparently synchronous time periods, if they are to be used in a regional tephrochronology.
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