The full programme book (PDF) - Royal Geographical Society

THEME 2: MEASURING TIME
A little goes a long way: the emergence of tephrochronology
Siwan M. Davies
College of Science, Department of Geography, Swansea University, Singleton Park, Swansea, Wales
Tephrochronology has developed into a widely-used and central technique for Quaternary
science. From its Icelandic origins in the study of visible tephra horizons, the technique
took a remarkable step in the late 1980s with the discovery of a 4000 year old microscopic
ash layer in a Scottish peat bog (Dugmore, 1989). Since then, the search for so-called
cryptotephra deposits (horizons that contain a low concentration of volcanic glass particles
that are, as such, invisible to the naked eye) in distal areas has gone from strength to
strength. Extraction techniques have been successfully adapted and modified to extend
the cryptotephra work into mineral-rich lacustrine and marine sediments, and ice-core
records. Indeed, a recent discovery demonstrates how just a handful of microscopic
volcanic particles can be traced over 7000 km from the volcanic source (Pyne-O'Donnell
et al., 2012). Instantaneous deposition of geochemically-distinct volcanic material over
such large geographical areas results in a powerful correlation tool with considerable
potential for addressing key scientific questions (e.g. assessing leads and lags in
palaeoclimate work, human dispersal and archaeological studies, volcanic ash-fall
frequency and marine reservoir offsets). An essential first step for facilitating this work is
the establishment of regional tephra frameworks that include well-constrained age
estimates and robust geochemical signatures for each volcanic event (e.g. Lowe et al.,
2008). With distal sites revealing a complex record of previously unknown volcanic events,
such frameworks are regularly refined and revised and, in some instances, it has become
apparent that some closely-timed eruptions have similar geochemical signatures, thus
presenting a challenge for tephrochronologists. As such, the search for unique and robust
geochemical fingerprints now hinges on rigorous single-shard analysis by electron
microprobe and Laser-Ablation ICP-MS. Historical developments, methodological
challenges and significant breakthroughs will be presented to chart the pivotal
contributions of UK and QRA scientists to the emergence and prominence of
tephrochronology.
Keywords: tephrochronology; cryptotephra; precise correlation; geochemical fingerprinting
Dugmore, A.J., 1989. Icelandic volcanic ash in Scotland. Scottish Geographical Magazine 105, 168-
172.
Lowe, J.J., et al., 2008. Synchronisation of palaeoenvironmental events in the North Atlantic region
during the Last Termination: a revised protocol recommended by the INTIMATE group. Quaternary
Science Reviews 27, 6-17.
Pyne-O'Donnell, S.D.F., et al., 2012. High-precision ultra-distal Holocene tephrochronology in North
America. Quaternary Science Reviews 52, 6-11.