Have local stages outlived their usefulness for the New Zealand Pliocene‐Pleistocene?

Abstract

Stratigraphic subdivision of the New Zealand Pliocene‐Pleistocene has its historical basis in biostratigraphy, especially in the shallow marine strata in the Wanganui and East Coast basins, North Island. Internationally, an astronomically calibrated, high resolution timescale is now well established for the Pliocene‐Pleistocene, based on predominantly precession‐controlled sedimentary cycles in the Mediterranean region, and the mainly obliquity‐controlled, high resolution, deep‐sea, benthonic oxygen isotope record. Naish and others have recently provided a similar Milankovitch‐frequency cyclostratigraphy for the Pliocene‐Pleistocene of New Zealand (last 3.6 m.y.), based on the Wanganui Basin record. This cyclostratigraphic record allows numeric ages to be estimated for at least 114 stratigraphic horizons in Wanganui Basin, which are not otherwise dated. Based on this record, we propose new definitions for the boundaries between New Zealand Pliocene‐Pleistocene stages. The new boundaries respect traditional biostratigraphic indicators, but are based upon objective markers, mainly magnetic polarity reversals. The two exceptions are the base‐Marahauan (equated with the international Pliocene‐Pleistocene boundary, at 1.81 Ma) and the base‐Haweran (equated with the base of the Rangitawa Tephra, at 0.34 Ma). The revised positions and ages for the age/stage and subage/substage boundaries, from older to younger, are: base‐Opoitian Stage, base‐Thvera subchron, 5.25 Ma; base‐Waitotaran Stage (= base‐Waipipian Substage), Gauss/Gilbert boundary, 3.60 Ma; base‐Mangapanian Substage, top‐Kaena Subchron, 3.03 Ma; base‐Nukumaruan Stage (= base‐Hautawan Substage), Matuyama/Gauss boundary, 2.58 Ma; base‐Marahauan Substage, Pliocene‐Pleistocene boundary, 1.81 Ma; base‐Castlecliffian Stage (= base‐Okehuan Substage), base‐Jaramillo Subchron, 1.07 Ma; base‐Putikian Substage, Brunhes/Matuyama boundary, 0.78 Ma; base‐Haweran Stage, base‐Rangitawa Tephra, 0.34 Ma.