New Zealand Pleistocene and late Pliocene glacio-eustatic cycles

Abstract

A correlation diagram relates the numbered oxygen isotope stages of Shackleton and Opdyke's oxygen isotope curve for core V28–239, as extended by Gardner, to Nukumaruan, Castlecliffian and younger sedimentary cycles in Hawke's Bay, southern Wairarapa, and Wanganui districts and to the flight of marine terraces (Castlecliffian and younger) recognised by Pillans near Wanganui. Local correlation is principally by biostratigraphy, but also by lithostratigraphy and fission-track dates on tephras. Important calcareous nannofossil datums for both local and international correlation are: (1) FAD of Gephyrocapsa sinuosa in the mid-Nukumaruan of the New Zealand region, both in DSDP site 284, just above the (base Olduvai) LAD of Discoaster brouweri, and in three on-land sequences (within the Olduvai at Mangaopari Stream); (2) LAD of Pseudoemiliania lacunosa, during isotope stage 12, last known in the Castlecliffian Upper Kai-Iwi Siltstone at Wanganui; and (3) FAD of Emiliania huxleyi during isotope stage 8, and recorded tentatively from the Waipuna Delta Conglomerate (Ngarino Terrace cover beds; Hawera Series) near Wanganui. Magnetic polarity is also used for external correlation. Most of the prominent oxygen isotop events in core V28–239 are inferred in New Zealand on-land sequences (about twenty cycles). The Wanganui area demonstrates an apparently unique occurrence of coeval marine terrace deposits and offshore marine rocks representing all major high sea levels between isotope stages 11 and at least 17. Nukumaruan sedimentary cycles recognised in eastern North Island are relatively complete, most inferred glacial periods being represented by shallow marine strata. In contrast, Castlecliffian and younger marine sedimentary cycles in southwestern North Island are less complete, each inferred interglacial deposit being bounded by disconformities. The difference between Nukumaruan and younger sedimentary cycles possibly supports the hypothesis of an increase in the amplitude of sea-level change about a million years ago. The Pliocene/Pleistocene boundary lies above the middle of the New Zealand Nukumaruan Stage.