Abstract

The Sackville Spur is a sediment drift feature that forms a northeastward extension of the Grand Banks continental slope between the 900 and 2500 m isobaths near latitude 48°N. At present, the Labrador Current (LC) and the Western Boundary Undercurrent (WBUC) appear to be the two major hydrodynamic forces controlling sedimentation patterns on the flanks of the spur. Near the upper part of the spur's north flank, a deep offshore component of the LC appears to be selectively winnowing silt and clay-size particles, leaving a lag deposit composed of about 43% sand-size material. The base of the north flank (≈2500 m) is in a zone in which sediments can be reworked by the fast-flowing core of the WUBC. Here surficial sediments are characterized by a relatively high percentage of fine (2–3graphic) sand and by a lower percentage of silt compared with sediments observed near the spur crest.Reflection seismic data suggest that current-influenced deposition, associated predominantly with bottom-sediment reworking by the deeper offshore component of the LC, has been active over the uppermost part of the spur since Late Miocene to Early Pliocene time. The initiation of deep LC flow at this time is marked by a distinctive angular unconformity near the base of the spur drift deposit. Following this erosional event, deposition caused rapid progradation of the spur to the northeast. The latest phase of the spur's evolution is characterized by (i) intermittent erosion with concomitant large-scale submarine sliding; (ii) smaller scale mass-flow deposition; and (iii) a distinctive southeastward shift of its depocentre toward the Flemish Pass.

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