Preface: Global tephra studies: John Westgate and Andrei Sarna-Wojcicki commemorative volume

Abstract

Tephras (from the Greek word tephra, meaning ‘ashes’) are the explosively erupted pyroclastic (fragmental) products of volcanic eruptions. They encompass all grain sizes ranging from fine dust (ash) to large blocks or bombs. Unless reworked, a tephra layer has the same age wherever it occurs and thus, once characterized or ‘fingerprinted’ by its mineralogical and geochemical properties, provides a time-parallel stratigraphic marker bed or isochron. Tephrochronology is the use of tephra layers as isochrons to connect sequences in different places by providing precise chronostratigraphic tie-points, and to transfer relative or numerical ages to such sequences where the tephras have been dated by radiometric, incremental, or age-equivalent dating methods (Alloway et al., 2006 B.V. Alloway, G. Larsen, D.J. Lowe, P.A.R. Shane and J.A. Westgate, Tephrochronology, S.A. Elias, Editor, Encyclopaedia of Quaternary Science, Elsevier, London (2006), pp. 2869–2898. Alloway et al., 2006).