ABSTRACT: Morphology of submarine canyons and channels on the central Scotian Slope.

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Abstract

Submarine canyons and channels are important conduits for carrying sediment from the outer shelf to the abyssal plain. The Scotian Slope lies approximately 200 km south of Nova Scotia and trends northeast/southwest, parallel to the modern coastline. South of Western Bank and Banquereau, the Slope is heavily incised by submarine canyons. In 2000, more than 20 000 square kilometres of multibeam bathymetry was collected on the central Scotian Slope between Mohican Channel and the Gully, from 150 to 3500 metres water depth. A series of groundtruth expeditions occurred over subsequent field seasons, which together with the multibeam data provide an excellent dataset for investigating continental slope processes. This study uses qualitative and quantitative geomorphology techniques to describe and interpret submarine canyons and channels on the Scotian Slope. The morphology of the central Scotian Slope ranges from planar in cross-section with little relief in the west, to concave-up in cross-section with irregular relief in the east. In the eastern part of the study area major submarine canyons and intercanyon divides are the dominant features. The canyons are dendritic and form distinct catchments which coalesce into large channels on the continental rise. A few canyons erode into the continental shelf, the Gully being the most severe example. Most canyon tributaries head on the upper slope in glacial till, however some head in water depths as great as 1000 metres. On some canyons there is less rill and gully development on the canyon walls and there is more evidence of seafloor retrogression. Between Mohican Channel and Verrill Canyon, the seafloor has a unique planar shape which is superimposed with continuous failure escarpments up to 100 metres in height. Previous studies have shown that this area has experienced repeated small-scale seabed failure during the Pleistocene, which may explain the distinctive shape. Evidence of seafloor retrogression is common on the upper slope in the western part of the study area, with failure scarps terminating in more competent outer shelf deposits. Linear channels with low relief are present and are continuous from the upper slope to the continental rise. A model is presented that relates canyon style to the major features of shelf crossing glaciation. We evaluate the relative importance of direct hyperpycnal flow from meltwater, sediment fallout from proglacial plumes, retrogressive slope failure, and sediment character of the upper slope in development of the canyon systems.

Bibliography of Canadian Geomorphology