Pleistocene marine terraces of the Wellington south coast – their distribution across multiple active faults at the southern Hikurangi subduction margin, Aotearoa New Zealand

ABSTRACT

Along the south coast of the North Island of New Zealand, elevated Pleistocene marine terraces provide evidence for vertical deformation associated with active crustal faults and the westward subduction of the Pacific Plate at the southern Hikurangi margin. We have reassessed the age and elevation of these terraces. Optically Stimulated Luminescence (OSL) data of their cover bed sediments (20 new ages) provide the first numerical ages for most of these terraces. Shore platform elevations have been surveyed using differential Global Navigation Satellite System (GNSS) measurements of the wave-cut bedrock straths underlying these terraces. These new data allow the terraces to be temporally correlated across the margin. Seven different-aged terraces were identified and mapped along the Wellington south coast; these are preserved discontinuously between the westernmost site at Tongue Point, and Ngawi near Cape Palliser, to the east. The OSL data indicate that most of these terraces formed at MIS 5a, 5c, 5e (Last Interglacial) and 7a. The terraces are best preserved within the Hikurangi margin forearc, where they decrease in altitude towards the west, indicating long wavelength, westward tectonic tilting. The terraces are locally offset by a number of active crustal faults, most notably the Wairarapa and Ohariu faults.

KEYWORDS:

• Pleistocene marine terrace
• MIS 5e
• interglacial
• tectonic uplift
• Hikurangi subduction margin
• active fault
• Wellington
• Wairarapa

Acknowledgements

The authors would like to thank Brad Pillans, John Begg and Tim Stern for helpful comments on an earlier version of this manuscript. Reviewers Brendan Duffy and Deirdre Ryan provided insightful suggestions which further improved this paper. We are grateful to John Chappell for thought-provoking discussions on marine terraces and OSL dating. We would like to thank the Earthquake Commission for funding (Grant No. 09/U576) to undertake this investigation. Thanks to the Greater Wellington Regional Council for providing LiDAR data, and to Andrew Rae of Victoria University of Wellington for managing this data. For assistance with fieldwork and data collection: Jim Driscoll, Anya Seward, Jane Chewings, Megan Korchinski, Liz Schermer and students from Western Washington University. We are grateful to the landowners and land managers along the south coast of the North Island, for access to their property, in particular to Hugh Prickett for his interest in this investigation. We dedicate this manuscript to John Chappell (1940–2018), a leader in the field of Quaternary Research, of uplifted marine terraces and the information they hold.

Data availability statement

The majority of the data that support the findings of this investigation are available within the article. Additional data is openly available on figshare; specifically, the full Optically Stimulated Luminescence technical report from the Luminescence Dating Laboratory, School of Geography, Environment and Earth Sciences Victoria University of Wellington (https://doi.org/10.6084/m9.figshare.16968556.v2), and Wellington south coast Pleistocene marine terrace shore platform location and elevation measurements (https://doi.org/10.6084/m9.figshare.17030009.v1)

Disclosure statement

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

Additional information

Funding

This work was supported by Earthquake Commission [Grant Number EQC 09/U576].