Depositional rate, grain size and magnetic mineral sulfidization in turbidite sequences, Hikurangi Margin, New Zealand

ABSTRACT

Sedimentological and rock magnetic analysis was performed on 67 turbidite samples recovered from Lithostratigraphic units I–III at IODP Site U1520 with the aim to characterise the sedimentary processes and post-depositional diagenesis within a Quaternary sequence in the Hikurangi Trough, New Zealand. Lithostratigraphic Unit I was rapidly emplaced with frequent turbidite deposition with high sedimentation rate (∼1.9 m/kyr). In contrast, in units II–III, the turbidites were finer grained and more thinly bedded, and were deposited at less than half the deposition rate of Unit I. The turbidites were classified into three clusters based on the magnetic properties. Clusters 1 and 2 are characterised by a high coercivity and SIRM/χ, but low to moderate B_cr/B_c. The recognition of gyroremanent magnetisation acquisition in their clusters indicates the diagenetic sulfidization. Cluster 3 was represented by low coercivity and SIRM/χ, but high B_cr/B_c, indicating lack of sulfidization. Restricted occurrence of Cluster 3 in Unit I may be ascribed to the high sedimentation rate, which prevents sulfidization at the sulfate–methane transition zone. Degree of sulfidization might be related with sedimentary features of turbidites in the trough, such as grain size, bed thickness and depositional rate.

KEYWORDS:

• Rock magnetic property
• grain size
• turbidite
• diagenesis
• Hikurangi Trough
• New Zealand
• IODP

Acknowledgements

This research used data and samples provided by the International Ocean Discovery Program (IODP). The authors are grateful to the science party and all technical staff of Expeditions 372 and 375 for assistance with the acquisition of samples and data processing, as well as for their contributions to the discussion of our findings, especially the co-chief scientists Phil Barnes, Ingo Pecher, Laura Wallace, and Demian Saffer. Phil Barnes and Lorna Strachan kindly shared unpublished data of the radiocarbon dating for making an early version of this manuscript. We also thank members of the sedimentology group of Expedition 375 for counting and measuring the turbidites onboard the research vessels. A.G. acknowledges funding through NWO DeepNL (Grant no. 2018.040) and KETEP-MOTIE (Grant no. 20168510030830).

Disclosure statement

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

Data availability statement

Shipboard data are available from the IODP database (http://web.iodp.tamu.edu/LORE/). The rock magnetic data that support the findings of this study are openly available in Figshare (https://doi.org/10.6084/m9.figshare.14456550).

Additional information

Funding

This work was supported by Korea Institute of Energy Technology Evaluation and Planning [grant number 20168510030830]; Nederlandse Organisatie voor Wetenschappelijk Onderzoek [grant number DeepNL 2018.040].