EVOLUTION OF PLIOCENE TO RECENT ABYSSAL SEDIMENT WAVES ON BOUNTY CHANNEL LEVEES, NEW-ZEALAND

Levees bordering Bounty Channel 900 km east of New Zealand accommodate a 400 m-thick sequence (maximum) of sediment waves that have formed since Pliocene times. These bedforms, with amplitudes of 2-17 m and wavelengths of 0.6-6 km occur in 4100-4900 m of water and were formed by turbidity currents, as indicated by their restriction to levee backslopes, the frequent occurrence of turbidites in cores and the preferential but not exclusive development of waves on the left-bank levee in accord with the Southern Hemisphere coriolis deflection. The wave field was instigated in the Late Pliocene when glacially lowered sea level allowed rivers draining the Southern Alps of South Island to discharge directly into Bounty Channel and its attendant canyons. The field grew vertically through the coalescence of small waves into larger bedforms that continually migrated across and up levee backslopes at an average rate of 5.6m/100 yrs. Wave growth decreased into the Late Pleistocene probably in response to progressive containment of turbidity currents as the relief of Bounty Channel increased to 200 m or more. The glacial periods of wave growth were interrupted by interglacial interludes of quiescence when the field was draped mainly by pelagic calcareous ooze. © 1990.