Tephrochronology and its application: A review

Abstract

Tephrochronology (from tephra, Gk "ashes") is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events. As well as utilizing the Law of Superposition, tephrochronology in practise requires tephra deposits to be characterized (or "fingerprinted") using physical properties evident in the field together with those obtained from laboratory analyses. Such analyses include mineralogical examination (petrography) or geochemical analysis of glass shards or crystals using an electron microprobe or other analytical tools including laser-ablation-based mass spectrometry or the ion microprobe. The palaeoenvironmental or archaeological context in which a tephra occurs may also be useful for correlational purposes. Tephrochronology provides greatest utility when a numerical age obtained for a tephra or cryptotephra is transferrable from one site to another using stratigraphy and by comparing and matching inherent compositional features of the deposits with a high degree of likelihood. Used this way, tephrochronology is an age-equivalent dating method that provides an exceptionally precise volcanic-event stratigraphy. Such age transfers are valid because the primary tephra deposits from an eruption essentially have the same short-lived age everywhere they occur, forming isochrons very soon after the eruption (normally within a year).As well as providing isochrons for palaeoenvironmental and archaeological reconstructions, tephras through their geochemical analysis allow insight into volcanic and magmatic processes, and provide a comprehensive record of explosive volcanism and recurrence rates in the Quaternary (or earlier) that can be used to establish time-space relationships of relevance to volcanic hazard analysis.The basis and application of tephrochronology as a central stratigraphic and geochronological tool for Quaternary studies are presented and discussed in this review. Topics covered include principles of tephrochronology, defining isochrons, tephra nomenclature, mapping and correlating tephras from proximal to distal locations at metre-through to sub-3 millimetre-scale, cryptotephras, mineralogical and geochemical fingerprinting methods, numerical and statistical correlation techniques, and developments and applications in dating including the use of flexible depositional age-modelling techniques based on Bayesian statistics.Along with reference to wide-ranging examples and the identification of important recent advances in tephrochronology, such as the development of new geoanalytical approaches that enable individual small glass shards to be analysed near-routinely for major, trace, and rare-earth elements, potential problems such as miscorrelation, erroneous-age transfer, and tephra reworking and taphonomy (especially relating to cryptotephras) are also examined. Some of the challenges for future tephrochronological studies include refining geochemical analytical methods further, improving understanding of cryptotephra dis...

Construction of volcanic records from marine sediment cores: A review and case study (Montserrat, West Indies)

“…There have been considerable advances in the methods used to detect, date and characterise volcaniclastic deposits in the last few decades (Froggatt, 1992;Turney et al, 2004;Blockley et al, 2005;Gehrels et al, 2008;Manville et al 2009;Lowe, 2011). However, subjective elements in the criteria used to identify a tephra layer deposited from an explosive volcanic eruption still remain.…”

“…Multiple studies utilise glass geochemistry to distinguish primary from reworked volcanic deposits, based on the amount of inter-clast chemical variability within one sample (Schneider et al, 2001;Kutterolf et al 2009;Lowe et al, 2011;Schindlbeck et al 2013). The premise of this hypothesis is that a large compositional scatter between clasts indicates clast origins from multiple volcanic events, and the deposit is therefore reworked.…”

“…The purpose of using glass chemistry in this paper is to assess how effectively it can discriminate reworked from primary eruption deposits.. Figure 7a uses a SiO2 vs CaO plot to illustrate this method in the same manner as used in other studies (Lowe et al, 2011). Figure 7a shows that glass chemistry alone is not useful for achieving the objectives listed above.…”

The cultural nature of tephra: ‘Problematic’ ecofacts and artifacts and the Barú volcano, Panamá

“…Tephra studies are increasingly important components of Quaternary research and provide a unique means to address palaeoenvironmental and archaeological chronologies (Lowe, 2011;Lowe and Alloway 2014). The precise relationship between key volcanic eruptions and the archaeological and environmental record can be highly problematic, however, even for heavily studied volcanic events such as the Bronze Age eruption of Santorini/Thera (e.g., Manning, 1999;Pearson et al, 2005;Friedrich et al, 2006;Manning et al, 2006).…”

Tephrochronology of core PRAD 1-2 from the Adriatic Sea: insights into Italian explosive volcanism for the period 200–80 ka

“…This approach is preferred to an ordinal classification, as it reduces confusion 132 and potential ambiguity should additional tephra layers be detected in subsequent research 133 (Lowe, 2011). …”