Isothermal plateau fission-track ages of tephra beds in an Early-Middle Pleistocene marine and terrestrial sequence, Cape Kidnappers, New Zealand

Abstract

Abstract At least nine rhyolitic eruptive events or sequences are interbedded with alternating marine and terrestrial sediments of Early-Middle Pleistocene age at Cape Kidnappers, New Zealand. The sediments represent one of the few high resolution glacio-eustatic sea level records in New Zealand. We have obtained ages of 0.99±0.09, 1.00±0.10, 0.86±0.05, and 0.79±0.06 Ma (in ascending stratigraphic order) for four prominent tephra beds, from isothermal plateau fission track dating of their glass shards. These ages are older than previous fission track determinations, but are in agreement with tephra correlations to other sections, Ar/Ar data, and magnetostratigraphy. However, the upper part of the sequence, previously interpreted as the Brunhes Chron, may have been affected by normal overprinting and is instead older. The tephra record suggests a higher frequency of eruptions than is indicated by the proximal ignimbrite record in the Taupo Volcanic Zone. The new tephra ages indicate that the section was deposited in the interval 1.0-0.65 Ma at a rapid average sedimentation rate of ca. 1 m/ka.