Coeval Transverse and Axial Sediment Delivery to the Northern Hikurangi Trough During the Late Quaternary

Abstract

Subduction trenches receive sediment from sediment gravity flows sourced from transverse pathways and trench parallel axial transport pathways. Understanding the interplay between axial and transverse sediment transport in shaping stratigraphic architectures is hindered by the episodic nature of sedimentary gravity flows and limited datasets, yet such insights are crucial for reconstructing sedimentary flow pathways and interpreting sedimentary records. We investigate sediment routing pathways to the northern Hikurangi Trough of New Zealand using a combination of multibeam, 2D and 3D seismic reflection and International Ocean Discovery Program core data from Site U1520. Site U1520's location downstream of axial and transverse conduits of sediment delivery makes it an excellent location to observe how these processes interact in deep marine settings. We characterise regional basin floor geomorphology and sub-surface architecture of the upper ~110 m siliciclastic sequence of the Hikurangi Trough deposited over the past ~42 ka (Seismic Unit 1; SU1). Sediment delivery to the trough is fed by sediment gravity flows sourced from both the shelf-incising transverse Māhia Canyon to the south-west and the axial Hikurangi Channel to the south. Flows sourced from these systems have a strong influence on the geomorphology of the region and are responsible for forming large-scale bathymetric features such as erosional scours and sediment waves. Sedimentary features identified within SU1 indicate that sediment transport via the transverse Māhia Canyon was more significant than that of the axial Hikurangi Channel throughout the last 42 ka, particularly during the last glacial period when sea levels were lower, and sedimentation rates were extremely high (up to ~20 m/kyr). This study emphasises the need for a nuanced consideration of transverse and axial systems and how they may influence sediment records and the geomorphic characteristics of trench systems.