Lacustrine sequences were obtained from Laguna Verde and Laguna Gemelas Este, two small lakes 43 located east of the southern Patagonian Ice Field and close to the village of El Chaltén in Argentinian 44 Patagonia. Four tephra layers were identified in each of these short sedimentary sequences and 45 characterised using individual glass-shard tephra chemistry to determine provenance. In order to 46 understand the impact of the tephra deposits on lake ecosystems, bulk sediment geochemistry and 47 diatom assemblages were analysed. Age-depth models for the cores were established by radiometric 48 dating using 137 Cs and 210 Pb measurements. 49

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We report the first observations of Holocene cryptotephra deposits in lacustrine sediments from mainland Australia. All counts of cryptotephra shards are presented, but we focus on two prominent peaks of dark coloured glass shards representing distinct cryptotephras within the sediments of Lake Keilambete, Victoria, southeast Australia. These two basaltic cryptotephras, aged 4589-3826 cal BP and 7149-5897 cal BP, may have derived from eruptions of Mts Gambier or Schank, South Australia. In addition, colourless shards, most likely of silicic composition and therefore unlikely to emanate from an Australian volcano were observed, suggesting a distant volcanic source beyond Australia. The presence of both the 'local' basaltic shards and the distal silicic shards highlights the potential to identify isochronous marker horizons in southern Australian sediments, thus potentially enabling a long-term goal of establishing a novel chronostratigraphic tool based on a cryptotephra network.