Abstract

Tephrochronology (the dating of sedimentary sequences using volcanic ash layers) is an important tool for the dating and correlation of sedimentary
sequences containing archives and proxies of past environmental change. In addition, tephra layers provide valuable information on the frequency and
nature of ash fallout from volcanic activity. Successful tephrochronology is usually reliant on the correct geochemical identification of the tephra which has,
until now, been based primarily on the analysis of major element oxide composition of glass shards using electron probe microanalysis (EPMA). However,
it is often impossible to differentiate key tephra layers using EPMA alone. For example, the Hekla AD 1947 and 1510 tephras (which are found as visible
layers in Iceland and also as ‘crypto-tephra’ microscopic layers in NW Europe) are currently indistinguishable using EPMA. Therefore, other stratigraphic
or chronological information is needed for their reliable identification. Raman spectroscopy is commonly used in chemistry, since vibrational information
is specific to the chemical bonds and symmetry of molecules, and can provide a fingerprint by which these can be identified. Here, we demonstrate how
Raman spectroscopy can be used for the successful discrimination of mineral species in tephra through the analysis of individual glass shards. In this study,
we obtained spectra from minerals within the glass shards – we analysed the microlites and intratelluric mineral phases that can definitely be attributed
to the tephra shards and the glass itself. Phenocrysts were not analysed as they could be sourced locally from near-site erosion. Raman spectroscopy
can therefore be considered a valuable tool for both proximal and distal tephrochronology because of its non-destructive nature and can be used to
discriminate Hekla 1510 from Hekla 1947.