Abstract
The Quaternary Period is characterised by significant and drastic worldwide climate change processes as the result of the repeated switch between glacial and interglacial conditions on Earth. Although isolated in the middle of the Pacific Ocean, New Zealand was also greatly impacted and this extended to offshore settings like the Great South Basin as well. There is little existing research into the Quaternary characteristics of the more distal parts of the Great South Basin that indicate its response to glaciations and deglaciations. Understanding sediment supply and transport behaviour of sediments associated with the Bounty Channel would lead to a deeper understanding of not just glaciation and deglaciation effects on coastal New Zealand in the Quaternary, but also aid in predicting how this system will react in the future to a rapidly warming world. Submarine channels serve significant roles as biodiversity hotspots, in the transfer of terrestrial sediment supply to the deep ocean, and as indicators of how much sea levels fluctuate during interglacials and glacials. They tend to form on passive margins beyond the shelf edge and can extend out to abyssal depths. A gap of knowledge exists in our understanding of the Quaternary migration of submarine channels and sediment supply to the Bounty Trough channel system in the Great South Basin. To fill in this knowledge gap, New Zealand Petroleum and Minerals (NZP&M) seismic and well data were used to interpret the shallow seafloor sediments of the Great South Basin to investigate the behaviour, evolution, and infill of paleo- and present-day submarine channels. The dataset includes over 3000 seismic lines covering a large area of the Great South Basin, including the Bounty Trough and its associated channel system. The IHS Kingdom analysis package was used for interpretation of the seismic data through the creation of seafloor and sub-seafloor time structure maps, and the investigation of Quaternary age features including paleochannels, sediment wave fields, sediment-infilled sub-basins, and clinoforms related to regression.
Results of the research included the observation of extensive paleochannel systems, a generally NW (toward the shore) migration of paleochannels adjacent to the Bounty Trough canyon, an unusual sediment-infilled sub-basin to the SE of the southernmost branch of the channel system, extensive sediment wave fields on the modern seafloor and subsurface, suggestions of gas hydrate escape from below the seafloor, and signals of normal regression near the coastline in the vicinity of the Clutha River. The amount of sedimentary infill found in a largely aggradational pattern in paleochannels, sedimentary sub-basins, and sediment wave fields suggests a significant period of sediment deposition from multiple sources, including the Deep Water Boundary Current, gravity flows and mass transport deposits, and riverine erosion along older seafloor surfaces. Suggestions for future research in the Great South Basin, particularly in relation to climate change, include mapping the extent and concentration of gas hydrates to evaluate the amount of potential methane release in a warming ocean, and further surveying of the normal regression signals found close to the Clutha River exit with upgraded and higher quality seismic data collection.