Abstract:
The Reinga-Northland Basin has been recently recognised in the previous decade as a frontier basin in regards to hydrocarbon potential. Despite this, there is limited knowledge of seafloor processes, pathways and sediment distribution within the area, which can provide vital clues in regards to hydrocarbon exploration without the significant investment of drilling wells. This study utilised high-resolution multibeam data (bathymetry and backscatter), 3.5 kHz sub-bottom profiler data, seismic data, sediment cores and surficial samples to determine recent sedimentary processes of a study area within the Reinga-Northland Basin. Morphometric analysis of geomorphological features (channel, sediment wave field, mass transport complex and pockmarks) was undertaken, with a method developed to characterise the geomorphology of specific features in the study area. Sediment waves display a wide variation of morphometric parameters and are hypothesised to be formed by bottom currents originating from a pulsating, southward migrating Tasman Front deflecting off the West Norfolk Ridge during periods of warmer climate. The low gradient (< 0.4ᵒ) channel within the study area is yet to reach equilibrium and is characterised by a convex shaped thalweg profile with multiple knickpoints. The channel is interpreted as the lower reaches of a channel-levee system fed by gravity flows from the South Maria Ridge. The mass transport complex flowing from the east to west supplies sediment from the Northern Kaipara Continental Margin and displays internal ridges suggesting multiple gravity flows have occurred. The area of the mass transport complex is approximately 2550 km2, and is likely to extend further towards the Herekino Bank. Pockmarks in the study area are interpreted to be related to fluid expulsion and have an elliptical morphology shaped by bottom currents. Sedimentological results indicate a CaCO3-rich, hemipelagic setting with a sedimentation rate of 33.8mm/kyr based on radiocarbon dating of foraminifera. This is a faster sedimentation rate than previously suggested. This thesis contributes to the modern geomorphology within deep marine basins on continental New Zealand. Seafloor features potentially indicative of a hydrocarbon reservoir at depth are documented. The methods developed here contribute to the morphometric analysis of submarine channels, pockmarks, sediment wave fields and mass transport complexes.