Correlation between the Warepan/Otapirian and the Norian/Rhaetian stage boundary: implications of a global negative δ¹³C_org perturbation

ABSTRACT

The Norian/Rhaetian boundary interval (Late Triassic) is characterised by significant biotic turnover and severe climatic changes. However, this boundary still awaits formal definition. We have investigated the δ¹³C_org record within a well-preserved marine sequence exposed in the Kiritehere section, North Island, New Zealand. This section was located at higher latitudes (above 60°S) during the Triassic, and is considered the best exposed section representative of the New Zealand Warepan/Otapirian stage boundary. This is a regional boundary pertaining to the Zealandia region of Gondwana; it is described in the New Zealand Geological Timescale (NZGT) and it has been recognised as being correlative with the Norian/Rhaetian boundary. Using an integrated chemo- and biostratigraphic approach, we have identified a negative δ¹³C_org shift close to the disappearance of the standard-sized monotids (fossil bivalves) in the Kiritehere section. We interpret this negative shift to be the same negative δ¹³C_org shift that has been proposed to define the base of the Rhaetian. However, the position of the negative δ¹³C_org shift in the Kiritehere section is ca. 6.40 m below the accepted position of the Warepan/Otapirian boundary, based on biostratigraphy. This δ¹³C_org isotopic shift, best thought of as a chemostratigraphic event, is regarded here as a global phenomenon.

KEYWORDS:

• Late Triassic
• Norian
• Rhaetian
• Warepan
• Otapirian
• boundary
• δ¹³C_org
• New Zealand
• Zealandia
• Gondwana

Acknowledgements

The authors warmly acknowledge constructive reviews by James Crampton, Lydia Tackett and Erica Crouch and thank them for their useful comments leading to a much-improved manuscript.

Data availability statement

A detailed description of data that support this study are openly available in the Supplementary material at doi.org/10.1016/j.earscirev.2020.103180 for Kiritehere and Pignola-Abriola sections, and at www.geosociety.org/pubs/ft2011.htm (GSA Data Repository item 2011051) for Kennecott Point section.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by New Zealand Government: [Grant Number C05X1103 to GNS Science, MBIE - Ministry for Business, Innovation and Employment]; Ministero dell’Istruzione, dell’Università e della Ricerca: [Grant Number PRIN 2017W2MARE].