ISOTHERMAL PLATEAU FISSION-TRACK AGES OF TEPHRA BEDS IN AN EARLY-MIDDLE PLEISTOCENE MARINE AND TERRESTRIAL SEQUENCE, CAPE-KIDNAPPERS, NEW-ZEALAND

At least nine rhyolitic eruptive events or sequences are interbedded w ith alternating marine and terrestrial sediments of Early-Middle Pleis tocene age at Cape Kidnappers, New Zealand. The sediments represent on e 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 f our prominent tephra beds, from isothermal plateau fission track datin g of their glass shards. These ages are older than previous fission tr ack determinations, but are in agreement with tephra correlations to o ther sections, Ar/Ar data, and magnetostratigraphy. However, the upper part of the sequence, previously interpreted as the Brunhes Chron, ma y have been affected by normal overprinting and is instead older. The tephra record suggests a higher frequency of eruptions than is indicat ed by the proximal ignimbrite record in the Taupo Volcanic Zone. The n ew 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. Copy right (C) 1996 INQUA/Elsevier Science Ltd