Late Quaternary Progradation and Sand Spillover on the Outer Continental Margin Off Nova Scotia, Southeast Canada

摘要

Three distinct sediment types have prograded seaward from the outer shelf to the slope and rise in the vicinity of Sable Island Bank southeast of Nova Scotia during late Quaternary time. On the slope, the oldest facies recovered in cores is a brown to brick red, irregularly stratified, pebbly-sandy-clayey silt. Locally it is covered by an olive gray, clayey silt with a low sand and pebble content. This more homogenous gray facies displays abundant biogenic structures. A third facies, a thin layer of very fine, gray sand and muddy sand, locally covers brown and olive gray sediments on the slope and upper rise. All three facies contain similar light, heavy, and clay mineral suites. The regional distribution of these facies has been determined by core traverses normal to the shelf edge, including one passing down the axis of The Gully (largest submarine canyon in the area), and another extending down the dissected slope off Sable Island Bank. The brown, late Pleistocene unit is exposed on the floor of The Gully and on its dissected deep-sea fan; postglacial bottom processes have kept younger sediments from accumulating in these areas. The brown beds also are exposed on the lower slope and rise off Sable Island in areas of slumping or nondeposition. The olive gray facies, late Pleistocene-Holocene in age, occurs primarily on the slope; it is thicker on flanks of slope valleys and thinner or absent on the divides. It is absent on part of the lower slope and upper rise. On the lower rise, tan mud with a coarse fraction rich in Foraminifera and shell debris may be the equivalent of the olive gray slope facies.