Submarine slides and submarine canyons on the continental slope off Canterbury, New Zealand

Abstract

The continental slope off the Canterbury Plains, New Zealand, is a progradational feature dissected by submarine canyons to the north and by submarine slides to the south. To the north, during lower Pleistocene sea levels, fine sand was transported from the continental shelf to the upper continental slope by strong, northward-flowing bottom currents. Mud in suspension was also carried beyond the shelf edge in large quantities. Transport of the sand down the slope by gravity flow processes, possibly localised in slide scars, caused the erosion of submarine canyons. Subsequent interception of longshore-transported sand and gravel by canyons reaching Pleistocene strand lines would have accelerated canyon erosion. To the south, deposition of fine sediment with minimal spill-over of coarse bed material has dominated the Late Pleistocene development of the slope. This slope is consequently free of deep corrasional features like submarine canyons, but is prone to failure by gravity sliding. A number of the slides appear to have been late Last Glacial or Holocene events. Those portions of the slope not incised by canyons or slide scars are locally indented by small depressions, many of which appear to be gullies. None of these physiographic features are controlled by deep-seated faults, although possible downwarping of the crust may have triggered the larger slides.