First Holocene cryptotephras in mainland Australia reported from sediments at Lake Keilambete, Victoria, Australia

Abstract

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.