Tephrochronology in Aotearoa New Zealand

ABSTRACT

Tephra deposits in Aotearoa New Zealand (ANZ) have been studied for >180 years. The now-global discipline of tephrochronology, which has some developmental roots in ANZ, forms the basis of a powerful chronostratigraphic correlational tool and age-equivalent dating method for geological, volcanological, palaeoenvironmental, and archaeological research in ANZ. Its utility is founded on the key principle that tephras or cryptotephras provide widespread isochrons in many different environments. In the first part of this article, we summarise the history of tephra studies in ANZ and then describe how tephras have been mapped, characterised, and correlated using field and laboratory-based methods. We document advances in geochemical fingerprinting of glass; tephra/cryptotephra detection and correlation by sediment-core scanning methods (e.g. X-radiography, CT imaging, XRF elemental analysis, magnetic susceptibility); statistical correlation methods; and dating of tephras/cryptotephras. We discuss the advent of ANZ cryptotephra studies (from mid-1970s) and their more-recent growth. The second part comprises examples of applications of tephrochronology in ANZ: climate-event stratigraphy (NZ-INTIMATE project); eruptive-event stratigraphy in the Auckland Volcanic Field; developments in the marine tephra record; advances in identifying, correlating, and dating old (pre-50 ka) tephras and weathered-tephra deposits; forming soils/paleosols on tephras; tephras and archaeology; Kopouatai bog tephrostratigraphy and palaeoenvironments; and volcanic-hazard assessments.

KEYWORDS:

• Tephra
• volcanic ash
• tephrochronology
• cryptotephra
• stratigraphy
• glass shards
• fingerprinting
• EPMA
• LA-ICP-MS
• tephra mapping and analysis
• statistical correlation
• geochronology
• age modelling
• radiocarbon
• radiometric dating
• archaeology
• upbuilding pedogenesis
• weathered tephra
• volcanic hazards
• TVZ
• CVZ
• Rotoehu Ash
• Kawakawa/Oruanui tephra
• Taupō tephra
• history of science
• New Zealand

Acknowledgements

We thank guest editor James Scott for inviting us to write this article for the IAVCEI (NZ) special issue. We are especially grateful to former students whose theses we have cited. Max Oulton is thanked for drawing many of the diagrams in the paper, Nic Ross (Hamilton Radiology) for scanning lake cores using CT imaging and for the images in Figure 9b, and Simon Nathan for providing Figure 3. John Stribling and Tehnuka Ilanko are thanked for information about A.W.O. Burrell, and Brent Alloway, Marlena Prentice, Paul Froggatt, and Kate Mauriohooho willingly provided very valuable comments on a number of topics in the paper. We especially thank reviewers Alan Palmer and James White for their insightful comments and suggestions that have markedly improved the paper. Helen Deayton of Taylor & Francis provided much-appreciated support during the article's production phase. Notable mention is due to Caitlin Buck, Irka Hajdas, and Maarten Blaauw who introduced us to the revelatory world of Bayesian age modelling. Hopkins acknowledges the NZ Marsden Fund Te Pūta Rangahau a Marsden for supporting her Marsden Fast Start project, ‘Cryptotephra: unearthing hidden eruptions from Taupo Volcanic Zone’ (MFP-VUW1809). Lowe acknowledges the Earthquake Commission (EQC) for supporting the project, ‘Hidden hazards: revealing volcanic ashfall hazards in the Waikato region by detecting and analysing cryptotephras in sediments’ (15/U713), the Marsden Fund for supporting two projects, ‘New Views from old soils: testing the reconstruction of environmental and climatic change using genetic signals preserved in buried paleosols’ (UOW1006), and ‘Earth-shaking insight from liquefied volcanic-ash (tephra) layers in lakes: using geotechnical experiments, CT-scanned lake sediment cores, and tephrochronology to map and date prehistoric earthquakes’ (UOW1902), and also the MBIE Endeavour Fund (Smart Ideas) for support for the project ‘Evaluating earthquake risk using liquefied volcanic-ash layers in lakes’ (UOWX1903). Marsden-Fund projects are administered by the Royal Society of New Zealand (Royal Society Te Apārangi). The paper is also an output of the Commission on Tephrochronology (COT) of the International Association of Volcanism and Chemistry of the Earth’s Interior (IAVCEI).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article [and/or] its supplementary materials. The data that support the findings of this study are also available from the corresponding author [JLH] upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by MBIE Endeavour Fund Smart Ideas: [Grant Number UOWX1903]; Marsden Fund Te Pūta Rangahau a Marsden: [Grant Number MFP-VUW1809]; Earthquake Commission: [Grant Number 15/U713]; Marsden Fund Te Pūta Rangahau a Marsden: [Grant Numbers UOW1006 and UOW1902].