New Zealand Journal of Geology and Geophysics abstracts

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Stratigraphy and chronology of the Stent tephra, a c. 4000 year old distal silicic tephra from Taupo Volcanic Centre, New Zealand

BRENT ALLOWAY

Department of Geology
University of Auckland, Tamaki Campus
Private Bag 92 019,
Auckland, New Zealand

DAVID J. LOWE

Department of Earth Sciences and
Geochronology Research Unit
University of Waikato
Private Bag 3105
Hamilton, New Zealand

R. P. K. CHAN

Department of Mathematics and Statistics
University of Auckland, Tamaki Campus
Private Bag 92 019
Auckland, New Zealand

DENNIS EDEN

Landcare Research N.Z. Ltd.
Private Bag 11 052
Palmerston North, New Zealand

PAUL FROGGATT

Research School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand

Abstract  Tephrostratigraphic and chronologic studies in two areas of the North Island have identified a previously unrecorded, thin, distal silicic tephra derived from the Taupo Volcanic Centre. In Taranaki, three radiocarbon ages of the uncorrelated tephra are consistent with the independent radiocarbon chronology obtained from enveloping Egmont-sourced tephras. In western Bay of Plenty, where the uncorrelated tephra is also directly dated, it is overlain by Whakaipo Tephra (c. 2.7 ka) and underlain by Hinemaiaia Tephra (c. 4.5 ka). From these sites in Taranaki and western Bay of Plenty, seven radiocarbon dates obtained on the uncorrelated silicic tephra yield an error-weighted mean age of 3970 +/- 31 conventional radiocarbon years B.P. The ages on the uncorrelated tephra (informally referred to as Stent tephra) from both areas are statistically identical but significantly different from those on both Waimihia and Hinemaiaia Tephras.

The occurrence of Stent tephra in Taranaki, c. 160 km upwind from the postulated source area, and in western Bay of Plenty, suggests that it represents the product of a moderately large plinian eruption. Until recently, its validity as a discrete eruptive event had been problematical, because a near-source equivalent deposit between Waimihia and Hinemaiaia Tephras was not recognised in the Taupo area. However, a revised stratigraphy proposed by C. J. N. Wilson in 1993 for eastern sectors of the Taupo area shows that multiple tephra layers were erupted from Taupo volcano between c. 3.9 and 5.2 ka. Of these newly recognised layers, unit-Q--the product of a moderately large eruption (>=0.15 km3) at c. 4.0 ka--is tentatively correlated with Stent tephra. Other eruptive units recognised by Wilson are either too old or too small in volume to be considered as likely correlatives.

Keywords  stratigraphy; tephra; Holocene; Taupo volcano; distal; Stent tephra; 14C dating; unit-Q

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