Reconnaissance of the upper continental slope off Sable Island Bank, Nova Scotia

Abstract

A bathymetric chart or the . continental. slope off Sable Island - . Bank was compiled from soundings released by the Canadian Hydrographic Service. The slope in this area is dissected by numerous valleys in the region directly adjacent to Sable Island Bank but changes abruptly to a featureless terrain in the region off the southwestern limit of the bank. During cruises aboard the CSS KAPUSKASING and the CNAV -- ·- SACKVILLE, a total of 21 piston cores were obtained. Analyses of the sediment cores included visual description, iriVestigation of internal structure through X-radiography, textural analysis, petrographic examination of the coarse fraction, heavy minerals, and clq fraction, and investigation of the distribution of foraminifera. This reconnaissance study has revealed three sediment types on the continental slope. The sediloonts are very similar mineralogically and are probabl;r derived from material transported from northern Nova Scotia and the Gulf of St. Lawrence region by glacial processes. Several periods of sedimentation are indicated on the eontinentaJ. slope. During the height of the vlisconsin lowering of sea level active erosion of the exposed shelf led to the rapid deposition of a sand and pebble rich, brown mud on the continental. slope. Following the rapid rise in sea level, the shelf was submerged, and the abundant supply of sed:i.llent was cut off. Slow deposition of fine sand and mud subsequently formed a l~r of grey sediment on the slope. Continued removal of fines from the shelf, and increasing bottom currents, produced a graduaJ. increase in the proportion of sand being deposited on the slope. A thin layer of relatively clean sand, foum at the surface in many parts o:f' the slope, suggests the intensification of tbis process in Recent time.