Late-Quaternary Icelandic tephras in Ireland and Great Britain: detection, characterization and usefulness

Abstract

Microscopic studies of late-Quaternary tephras from Iceland yield a detailed tephrochronology in deposits of the British Isles, where the quantities of volcanic glass employed are much less than those used to construct almost any other late-Quatemary tephrochronology. We summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in Ireland, including those which comprise an outline historic tephrochronology for Ireland. The paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical. Tephras in other parts of the British Isles and Europe are used, with those in Ireland, to demonstrate further applications of tephrochronology, especially for dating deposits where other dating methods (e.g., radiocarbon) have proved difficult.