Introduction

Since 1953 the Pliocene–Pleistocene boundary in New Zealand has been set at the base of the Nukumaruan (regional) Stage because that coincides with the abrupt first appearance of the subantarctic bivalve Chlamys delicatula (Hutton) in marine sequences of central New Zealand. However, it is now estimated, on the basis of biostratigraphic, magnetostratigraphic, and radiometric data, that the Nukumaruan commenced at about 2.4 Ma and ended about 1.3 Ma and that the Olduvai subchron approximately coincides with the middle of the Nukumaruan. In the stratotype Nukumaruan, and in correlative sections, a marked lithologic change (interpreted as the result of glacioeustatic regression) following the first appearance of Gephyrocapsa sinuosa Hay and Beaudry may be correlative with the top of the Olduvai and with the Vrica boundary-stratotype.

Historical background

In New Zealand, the regional stages for Upper Pliocene to Middle Pleistocene strata, in upward sequential order, are Waipipian, Mangapanian, and Nukumaruan. The Nukumaruan Stage is sometimes divided into the Hautawan and (above) Marahauan substages. More or less continuous marine and nonmarine sequences extend from the Pliocene into the Pleistocene in various parts of the country. Internal correlation between the sequences is poor, and for external paleontological correlation, for example with Italy, only the marine sequences are of value. Modern reviews of the Pliocene–Pleistocene boundary have been published by Vella (1975), Jenkins (1975), Hornibrook (1976), Edwards, Hornibrook, and Te Punga (1981), and Te Punga (1981).