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 of36 named late Quaternary (~. 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.

Re‐identification of c. 15 700 cal yr BP tephra bed at Kaipo Bog, eastern North Island: Implications for dispersal of Rotorua and Puketarata tephra beds

“…The glass compositions, together with biotite analyses, radiocarbon ages, and stratigraphic position, strongly support correlation to Rotorua Tephra now recognised to have abimodal glass composition. The age of c. 13 100 14 C yr BP (= c. 15 700 cal yr BP) estimated for the tephra bed at Kaipo using sedimentation rates and tephrochronology (Lowe et al 1999) is consistent with the pooled radiocarbon age of Rotorua Tephra of 13 080 ± 50 (n = 10) reported by Froggatt & Lowe (1990). The new correlation of the Rotorua Tephra at Kaipo eliminates the requirement to either revise the age of Puketarata Tephra or to invoke a scenario of two "Puketarata Tephra" eruptions occurring c. 1000 yr apart, as was tentatively suggested by Lowe et al (1999).…”

“…Previous studies have shown that it has a distinctive glass composition with high FeO and CaO (>1.2 wt%) and relatively low K 2 O (c. 3 wt%), in comparison with other OVC-derived high-silica rhyolite tephra beds (e.g., Lowe 1988b hypersthene + hornblende + augite ferromagnesian mineral assemblage (FMA) (Froggatt & Lowe 1990), and a relatively high eruption temperature (c. 850°C) has been estimated from Fe-Ti oxide data (Shane 1998). However, biotite has been recorded in the upper part of proximal Rotorua fall sequences (Froggatt & Lowe 1990). Biotite is common in distal Rotorua fall deposits, such as in lake deposits in the Waikato region, where it comprises c. 10% of FMA (Lowe 1988a), and in Onepoto Basin in Auckland (Fig.…”

A radiocarbon age determination for Mount Edgecumbe (Putauaki) volcano, Bay of Plenty, New Zealand

“…The age of the Whakatane Tephra at 4830 ± 20 yr B.P. (Froggatt & Lowe 1990) gives the age of the base of the section, and the top of the section is older than the Taupo Tephra at 1850 ± 10 yr B.P. Isopach maps (Vucetich & Pullar 1964) also indicate that only traces of Waimahia Tephra (3280 yr B.P.)…”

“…and 3280 yr B.P. (Nairn 1981;Froggatt & Lowe 1990). Nairn (1995) has recently reported an age of 2400 yr B.P.…”

“…(Froggatt & Lowe 1990), has a minimum thickness of 600 mm, and comprises a mottled golden brown to yellow brown pumice lapilli. It is well sorted with an average clast size of 5-8 mm and occasional 40 mm elongate pumice clasts.…”