Stratigraphy of the Kos Plateau Tuff: product of a major Quaternary explosive rhyolitic eruption in the eastern Aegean, Greece

Abstract

The Kos Plateau Tuff (KPT) erupted during a moderate-volume explosive rhyolitic event approximately 161 ka from a source south of Kos in the eastern Aegean sea. Six major stratigraphic units have been identified, from A at the base, to F, uppermost. Unit A is a widespread vitric ash fall layer that is thickest (1.5 m), and most extensive, southeast of the source. Unit B is a 1- to 2-m-thick, low-angle cross-stratified armoured pumice lapilli and ash layer found on Kos. Unit C resembles unit B but includes a greater abundance of lithic lapilli, less fine ash, is only diffusely stratified and is on Kos and west of the source. Unit D includes a sequence of three non-welded, 1- to 20-m-thick ignimbrites that extend radially >38 km from the source in areas of low topography. Unit E is a sequence of two non-welded, 3- to 8-m-thick ignimbrites which occur radially from the vent regardless of topography, >64 km from source. Unit F has a 6-m-thick, basal, low-angle cross-stratified armoured pumice lapilli and ash part probably deposited radially from source. The upper part of unit F is a widespread >1-m-thick vitric ash fall layer, found to at least 50 km from the source. These six units represent a change in eruptive conditions from initial and final phreatomagmatic activity depositing fallout and internally stratified pyroclastic density current deposits to "dry" explosive during the more intense phases of the eruption which generated ignimbrites.