Sedimentation since 140 ka in Te Tai-o-Aorere Tasman Bay, Aotearoa New Zealand

ABSTRACT

Late Pleistocene and Holocene sedimentation records changes in glacio-eustatic cycles, oceanography, active tectonics, and sediment supply. Here, we use high-resolution seismic-reflection profiles in Te Tai-o-Aorere Tasman Bay to investigate sedimentary deposit distributions associated with sea-level cyclicity over ∼140 ka. We identify nine seismic stratigraphic units below the inner continental shelf, interpret their character based on stratal relationships and acoustic properties, and infer ages using global sea level. The sequence includes stacked deposits and unconformities associated with the shifting shoreline over glacial cycles. Prominent erosional features include a lowstand ravinement surface and two transgressive surfaces formed during sea-level rise following the last two glacial maxima of ∼20 ka and ∼140 ka. The youngest surface marks the base of post-glacial sediment accumulated since ∼12 ka in the study area. Post-glacial sediment includes five seismically mappable units, covering an area of ∼1400 km² and deposit volume of ∼9 km³. Time-averaged sediment accumulation rates are estimated to range from a maximum of ∼1.6–2.8 m/kyr to ∼0.5–0.9 m/kyr. Sequence stratigraphy interpreted in Te Tai-o-Aorere Tasman Bay is representative of accumulation in a relatively wide-shelf, sheltered inner bay setting supplied by mountainous catchments, and provides stratigraphic context necessary for future stratigraphic and tectonics studies.

KEYWORDS:

• Seismic stratigraphy
• sedimentation
• sea level
• fluvial
• shallow marine
• post-glacial
• last glacial maximum
• Te Tai-o-Aorere Tasman Bay

Acknowledgements

We gratefully acknowledge the Ministry of Business, Innovation & Employment (MBIE) for funding through an Envirolink Medium Advice Grant 2209-NLCC120 to facilitate knowledge transfer to Te Kaunihera o Whakatū Nelson City Council and Te Kaunihera o Te Tai-o-Aorere Tasman District Council. The National Institute of Water and Atmospheric Research (NIWA) Subaqueous Geological Hazards and Marine Geological Resources programmes provided additional funding through MBIE Strategic Science Investment Funds. We thank the Nelson City Council and Tasman District Council for their partnership and interest in sediment accumulation in Te Tai-o-Aorere Tasman Bay, particularly Vikki Ambrose and Rob Smith. We gratefully acknowledge the NIWA and NIWA Vessels team that acquired the high-resolution seismic-reflection profiles across Te Tai-o-Aorere Tasman Bay in August 2021. We also thank Mike Johnston for his correspondence regarding onshore geology and stratigraphy, and fruitful discussions with Paul Wopereis (Beca) and Sean Handley (NIWA). The manuscript was improved by journal reviews from Dr Andrew La Croix and an anonymous reviewer, and guidance offered by the Associate Editor, Dr Lorna Strachan.

Data availability statement

Data are archived at NIWA, and derived data supporting the findings of this study can be made available upon reasonable request.

Disclosure statement

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

Additional information

Funding

This work was supported by Ministry of Business, Innovation and Employment [Grant Number Envirolink Medium Advice Grant 2209-NLCC120]; National Institute of Water and Atmospheric Research [Grant Number Hazards Programme and Marine Geological Processes].