The Karitane Canyon : a submarine valley cut into the Otago continental shelf

Abstract

High resolution sub-bottom reflection seismic profiles, sediment sample analysis and visual observation of the Karitane Canyon are correlated with multichannel seismics, known sediment distribution patterns and information from the wildcat exploration well Galleon-1 to compose an account of the structure and evolutionary history of the Karitane Canyon in relation to the Otago shelf.

The sedimentary pathways on the southeastern coast of New Zealand, through which sediments derived from central and eastern Otago travel in their transition from inland areas to the deep sea, comprises the Otago Submarine canyons at the shelf break channelling sediment down the Bounty Channel via the Bounty Trough until it ultimately deposits on the Bounty Fan Complex. This system is known to have existed for around 55 million years. The Karitane Canyon is one of the submarine canyons that constitutes the Otago Fan Complex.

Evidence presented here from high resolution sub-bottom seismic profiles collected for this study suggest the Karitane Canyon has been actively channelling sediment downslope for at least 2.4 million years, and possibly for as long as 4.2 Million years, in response to a changing tectonic regime during the Late Cenozoic. Large-scale foresets, progradational clinoforms, drape structures, and erosional surfaces and channels are all features that occur in these profiles. Deposition of relatively thick Pleistocene sequences over the shelf break is controlled by changes in relative sea level due to eustatic sea level fluctuations and the local tectonic situation. Seismically reflective strata identified in high resolution sub-bottom profiles are correlated with the wildcat exploratory well Galleon-1 for lithological and age data. Remote Operated Vehicle (ROV) footage of five investigative dives gives visual confirmation of the nature of sediment on the sea floor, and biological colonization of outcrop at the head and in the walls of Karitane Canyon.

Fossil tributary channels enter the open valley that is the Karitane Canyon of today all the way from the inner shelf toward the head (directly off Pleasant River), to the shelf break. These channels are in the order of 170 m to 190 m deep and up to 1.5 km wide. Many of the well preserved channels appear to be related to the last major glacial period of the Pleistocene as they often cut through Pliocene to Pleistocene strata.