Abstract:
The Hikurangi Channel, which is located east of New Zealand, is one of the largest submarine channels in the world. Submarine channels are important for transporting sediment from the mountains to the deep ocean. A large amount of the sediment to the Hikurangi Channel enters from the Kaikoura and the Cook Strait canyons, and then flows for 2000 km through the channel in the form of turbidity currents. A part of the Hikurangi Channel flows adjacent to the Hikurangi Subduction margin. This study uses 3 channel cores, and 3 adjacent levee cores, spanning a distance of 630km, to characterise the turbidite events seen in the channel and the levee, determine changes in these events going down the channel, and changes between the channel and levee. This project also aims to determine the recurrence interval of turbidite events seen in the Hikurangi Channel and levee, and discuss if this region is suitable for turbidite paleoseismology. Methods and data used in this project include visual logging, laser grain size, carbonate content analysis, percentage total organic matter, X-ray diffraction (XRD), Computerized Tomography (CT) Scans, magnetic susceptibility, and bulk density. Bathymetry data was also used to determine changes in channel morphology going down the channel, and between the channel and the levee. The sediment seen in these cores were divided into background sediment and event deposits, depending on the proportion of sand and very coarse silt. The dominant flow process seen in the Hikurangi Channel were turbidity currents. The channel width and depth reduced going away from the Kaikoura Canyon, which affected the turbidity currents, and in turn, the turbidites that were deposited in the channel and on the levee. Event deposits were either normally graded, or showed no grading, and also showed sedimentary structures such as planar and convolute laminations. The deposits fit models suggested by Bouma (1962), Piper (1978), Stow and Piper (1984), and Talling et al. (2012). Going down the channel, the grain size of the event deposits reduced, but more of the turbidite was preserved. The levee also showed finer grained event deposits, which were interpreted to have deposited due to flow stripping and overspill from the main channel. Recurrence intervals calculated ranged from 155-339 years, the higher of which were similar to recurrence intervals calculated by previous turbidite paleoseismology studies, or calculated by onshore paleoseismology. Recurrence intervals decreased going away from the Kaikoura Canyon, and this may be because deposits in the more distal locations represent seismic activity along larger sections of the Hikurangi Margin, and would record more frequent seismic activity. Since more of the event deposit was seen at distal locations, this study suggests that these locations would be ideal for future turbidite paleoseismology studies, as the deposit is less likely to be eroded away.