Abstract
Submarine canyons are well documented, both around New Zealand and globally, but questions remain around the processes involved in their formation and evolution as well as around how their morphology reflects their developmental history. The Waitaki Canyon, located at the edge of the passive Otago Shelf in the Canterbury Basin, southeast New Zealand, presents an opportunity to investigate the near-surface features associated with a shelf-indenting submarine canyon using high-resolution seismic data.
One such high-resolution survey was conducted in early 2015, collecting approximately 270 km of boomer seismic data in a high-density survey pattern centred at the head of the Waitaki Canyon. Approximately 40 km2 of the seafloor bathymetric data was also collected during that cruise. These data were analysed, along with approximately 100 km of boomer seismic data from a previous survey in the area and a selection of lower resolution seismic data from surveys conducted by the hydrocarbon industry, to investigate the subsurface structures in the vicinity of the Waitaki Canyon for evidence of changes in the canyon’s morphology throughout the Quaternary Period.
South of the Waitaki Canyon, a large (several kilometres across) asymmetrical system of infilled paleochannels is intersected by a canyon-parallel survey line and canyon-perpendicular lines. Several high-order sequence boundaries are identifed throughout the survey area, and a region of seafloor depressions is observed on a ridge near the head of the canyon.
Seismic reflections from the outer parts of the across-shelf survey lines are generally conformable, and do not show evidence of significant lateral migration of the canyon’s point of incision. The preferred interpretation of the stratigraphy and structures imaged in the data is that they represent the poorly preserved upper reaches of a series of paleochannels that had their heads somewhere west of the present canyon head and curved, or kinked, in very shallow S-shapes to rejoin the present path of the canyon. The canyon-parallel survey line thus intersects this kink and then approximately follows the centreline of the infilled channel, resulting in an asymmetric subsurface feature. The more recent symmetrical features are interpreted as non-axial tributaries or vestigial remains of this larger paleochannel.
This research has uncovered previously unknown features related to the Waitaki Canyon; however, more work is necessary to fully understand the relationship of those features to the present-day form of the canyon and the processes that were involved in their development.