Shelf to Deep-Sea Sediment Transportation in The Gully Submarine Canyon Off Nova Scotia: ABSTRACT

Submarine canyons on the Atlantic continental margin off northeastern North America received large amounts of fluvial and fluvio-glacial sediment from emerged shelves during glacial stages. It has been stated that the supply of sediment to canyon heads, especially to those located far from coast lines, was virtually cut off after the Holocene sea-level rise, and that at the present time there is little sediment movement down these canyons. An examination of numerous piston cores collected in The Gully, the largest canyon on the highly dissected continental slope off Nova Scotia, Canada, indicates that the above generalizations do not apply to all canyons of this region. The Gully heads on the outer Scotian shelf between Sable Island and Banquereau Banks, more than 100 nautical miles from the mainland. The Gully trends downslope southeastward in sinuous fashion for a distance of 35 miles to a depth of about 1,400 fathoms. The canyon is V-shaped and the walls are steep with gradients of 1 on 2. The longitudinal gradient ranges from 1 on 9 to 1 on 18. Small, precipitous tributary canyons enter the main canyon, especially along the west wall. Long cores collected at the base of the slope show an upward change in coloration from red (reworked till origin) to gray and olive (post-glacial). The number of coarse strata increases with depth, indicating that sediment rates decreased after the last rise in sea-level. However, the sediment sequence along the canyon length is proof of modern active sedimentation. Lenses of relatively clean sand in the upper reaches and near the steep walls of lateral tributary canyons are clearly derived from adjacent banks on the basis of minerology and faunal composition. Normal bottom currents, slumps, and sand flows probably moved these materials. In the same areas, contorted lenses of silty and sandy clay abound; localized slumping toward the canyon axis is the most important downslope transpo tation process. Pockets of sand and gravel, lying above mud in the canyon axis, and scour structures indicate that coarse clastics presently are being funneled downslope along the axis. Graded layers, 1-10 centimeters thick, are uncovered within the canyon and correlation is not possible between adjacent cores. Turbidity currents presumably are active in moving some material to the deep sea but, in this area, are of lesser importance than either slumps or bottom currents. End_of_Article - Last_Page 482------------