A review of late quaternary silicic and some other tephra formations from New Zealand: Their stratigraphy, nomenclature, distribution, volume, and age

Abstract

The stratigraphic relationships and distribution of 36 named late Quaternary (≤c. 50 000 yr B P.) silicic tephra formations, erupted from 4 volcanic centres—Okataina, Taupo, Maroa, and Tuhua (Mayor Island)—are presented. The stratigraphy and status of several other named late Quaternary tephras are also discussed. This compilation brings together all the data, currently scattered through many publications, to make tephrostratigraphy more accessible and more easily used. The nomenclature of tephra formations is discussed and some rationalisations are suggested. The term “tephrology” is suggested as an appropriate title for the field of tephra studies. The deletion of grain-size (ash, lapi1li), shape (breccia), and lithologic (pumice) terms from all formation names is recommended, as is standardisation on a “Tephra Formation” formal Several tephra layers not previously formally named, or without designated type sections, are defined. The dominant ferromagnesian mineral assemblage of each tephra formation has been compiled as an aid to tephra identification. All available radiocarbon ages (384) on each tephra formation are presented, and each age is assessed for reliability in dating the eruption of that tephra. The standard-deviation weighted mean age of the reliable ages has been determined as the best current estimate of the age of each tephra. At least 10 tephra formations have no reliable ages, and efforts should be made to date these. © Crown 1990.