New Zealand Journal of Geology and Geophysics abstracts
The status of local “stages” in the New Zealand Pliocene-Pleistocene
R. M. Carter
Marine Geophysical Laboratory
James Cook University
Townsville, Australia
and
School of Geological and Environmental Science
University of Adelaide
Adelaide, Australia
bob.carter@jcu.edu.au
The best hope for defining the true boundaries through all of the
New Zealand Late Neogene is to use radiometric and paleomagnetic dates
to calibrate sequences at appropriate places, and thus enable the use
of endemic fossils as well as the few useful cosmopolitan ones.
(Paul Vella 1975, p. 91)
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.
Keywords stratigraphic classification; age; stage;
oppelzone; Pliocene-Pleistocene
G04028; Received 18 July 2004; accepted 15 August 2005; Online
publication date 10 October 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
623–639
0028–8306/05/4804–623 © The Royal Society of New Zealand 2005
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