Magnetostratigraphic, lithostratigraphic and tephrostratigraphic constraints on Lower and Middle Pleistocene sea-level changes, Wanganui Basin, New Zealand

Abstract

Wanganui Basin, North Island, New Zealand, contains a complex sedimentary record of Lower and Middle Pleistocene sea-level changes. Palaeomagnetic results allow identification of the Matuyama/Brunhes transition, the Jaramillo Subchron and the Cobb Mountain Subchron. Correlations of rhyolitic tuff horizons across the basin are consistent with magnetostratigraphic correlations between sections. Isothermal plateau fission-track (ITPFT) ages of 1.05 ± 0.05 Ma and 1.63 ± 0.15 Ma on two tuffs (Potaka Pumice and Pakihikura Pumice, respectively) are consistent with the interpreted magnetostratigraphy and also with the astronomically tuned timescale of ODP Site 677. Magnetostratigraphy and ITPFT ages allow correlation of sedimentary cycles at Wanganui with odd-numbered oxygen isotope stages 17–31 in deep-sea cores. The stratotype section for the New Zealand Castlecliffian Stage is shown to be incomplete relative to other studied sections in the basin. Below stage 31, the character of the cyclothems changes at Wanganui, from marine dominated, to a greater representation of non-marine and estuarine strata. This change may be partly related to a change in amplitude and frequency of climatic cycles identified in oxygen isotope records, but the primary cause is likely to be increased basinal uplift.