Carter, R.M. (2005) The status of local “stages” in the New Zealand Pliocene-Pleistocene. New Zealand Journal of Geology and Geophysics, 48 (4). pp. 623-639.

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Abstract

Three different systems of nomenclature are in use for New Zealand’s Pliocene-Pleistocene rocks: marine stages, glacial stages (and advances), and international chrons and isotope stages based upon magnetic and oxygen isotopic criteria, respectively. The New Zealand marine stages, created by J. Allan Thomson in 1916, have evolved largely as biostratigraphic entities despite their chronostratigraphic appellation, and the scheme remains in active though ambiguous use. Over the last 20 yr, international magnetic and isotopic subdivisions have become widely adopted, driven by the availability of long offshore cores (DSDP Site 594, ODP Sites 1119, 1123), the reinterpretation of classic sections in eastern and western North Island (Mangaopari and Wanganui Basins), and the refinement of tephrochronology and other modern dating methods. One result is that the onland glacial stage scheme is falling into disuse, replaced by marine isotope stage (MIS) terminology. Meanwhile, attempts to provide rigorous definitions for the marine stages via Local Standard Stratotype-section and Point (LSSP) markers have ended in disagreement, with some researchers (e.g., Carter & Naish) favouring the use of objective ash bed or magnetic reversal markers as stage boundaries, and others (e.g., Beu, and Scott) preferring to retain traditional biostratigraphy. A fundamental distinction must be drawn between the definition of stages and their correlation. The errors inherent in the different criteria which are used for these operations in the Pliocene-Pleistocene are discussed. It is recommended (following QMAP practice) that international magnetic reversal and oxygen isotope divisions be used for referring to the age of New Zealand Pliocene-Pleistocene rocks back to 4 Ma, and perhaps beyond to the base of the Pliocene (c. 5.2 Ma). If they are to continue in usage, the local marine stages should have their historical meanings preserved by either: (1) rigorous definition as ages, using LSSP which are based on testable, objective criteria; or (2) reversion to use as biostratigraphic zones (oppelzones), with the implications that they may possess indeterminate (“fuzzy”) boundaries and have different age spans in different places.

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