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A Revised Calibration of the New Zealand Geological Timescale: NZGT2015

Abstract

The New Zealand Geological Timescale (NZGT)is a regional geochronological timescale for the Permian to Pleistocene and comprises a sequence of stages defined in New Zealand outcrop sections. The local stages have served an important role in fine-scale geological mapping since the mid-20th Century, and continue to provide a standard for stratigraphic subdivision by integrating biostratigraphic data from various fossil groups with other stratigraphic criteria (Cooper 2004). Many of the most useful fossil groups for subsurface exploration in New Zealand Mesozoic-Cenozoic basins have essentially local biogeographic distribution, or local ranges which differ from those of other regions because of differences in paleoclimate or ocean circulation, so the sequence of local stages which is closely tied to local fossils provides a more internally consistent, precise, and refined chronostratigraphy for routine use than international stages. Nevertheless, correlation with the International Geological Timescale (IGT) is required for communication with the international community, and age-calibration of stage and substage boundaries for estimation of rates of geological processes and correlation with numerical age data from radiometric and other methods. The status of the New Zealand stages is reviewed in a new publication (Raine et al. 2015) focussed on age-calibration of the stage boundaries. The revised calibration is based on calibration of the IGT by Gradstein et al. (2012), and is consistent with the International Chronostratigraphic Chart (Cohen et al. 2014). In the Cenozoic, calibration has relied mainly on correlation of planktic bioevents with the Geomagnetic Polarity Timescale (GPT), with input also from tephrochronology and isotope stratigraphy; in Cretaceous and older stages, the main approach has been biocorrelation of stage boundary and intra-stage bioevents with the IGT, with minor input from radiometric dating, carbon isotope stratigraphy and the GPT. References: Cooper, R. A. 2004. Institute of Geological and Nuclear Sciences monograph 22. Cohen, K.M.; Finney, S.C.; Gibbard, P.L. 2014. International Chronostratigraphic chart v 2014/10. International Subcommission on Stratigraphy. Gradstein, F.M.; Ogg, J.G.; Schmitz, M.D.; Ogg, G.M. 2012. The geological time scale 2012. Elsevier B.V., Oxford, U.K. Raine, J.I.; Beu, A.G.; Boyes, A.F.; Campbell, H.J.; Cooper, R.A.; Crampton, J.S.; Crundwell, M.P.; Hollis, C.J.; Morgans, H.E.G. 2015. GNS Science Report 2012/39.