D. Calvin Campbell

Near-surface geology and sediment-failure geohazards of the central Scotian Slope

The central Scotian Slope demonstrates a complex seafloor morphology superimposed on a regional gradient of 24 across the margin. The west-central Scotian Slope is characterized by a relatively smooth seafloor, but with numerous 1080-m (33260-ft)-high escarpments representing slide failure scars. In the east, the seafloor is highly dissected by canyons. Throughout the region are scars and deposits of sediment mass failures, including retrogressive headwalls, rotational slumps, slides, creep, debris-flow deposits, and turbidites.The complexity of failure styles and triggering mechanisms identified underscores the need for comprehensive site assessments for situating seabed facilities. Critical factors that need to be taken into account include local terrain analysis and shallow subbottom stratigraphy. Slope-stability analysis has shown the surface sediment to be statically stable, except on steep escarpments and canyon walls. There is evidence, however, of sediment failures that approximately correlate to glacial advances (2512, 75, and 130 ka), providing some clue as to potential triggering mechanisms. Sparse, passive-margin, tectonic earthquakes, however, are the likely cause for large-scale, regionally correlated failures and failure escarpments.

Late Quaternary history of contourite drifts and variations in Labrador Current flow, Flemish Pass, offshore eastern Canada

Contourite drifts of alternating sand and mud, shaped by the Labrador Current, formed during the late Quaternary in Flemish Pass seaward of the Grand Banks of Newfoundland, Canada. The drifts preserve a record of Labrador Current flow variations through the last glacial maximum. A high-resolution seismic profile and a transect of four cores were collected across Beothuk drift on the southeast side of Flemish Pass. Downcore and lateral trends in grain size and sedimentation rate provide evidence that, between 16 and 13 ka, sediment was partitioned across Beothuk drift and the adjacent Flemish Pass floor by a strong current flow but, from 29 to 16 ka, sedimentation was more of a blanketing style, represented by draped reflections interpreted as being due to a weaker current. The data poorly resolve the low sedimentation rates since 13 ka, but the modern Labrador Current in Flemish Pass is the strongest it has been in at least the past 29 ka. Pre-29 ka current flow is interpreted based on reflection architecture in seismic profiles. A prominent drift on the southwestern side of Flemish Pass formed above a mid-Miocene erosion surface, but was buried by a mass-transport deposit after the penultimate glacial maximum and after drift deposition switched to eastern Flemish Pass. These findings illustrate the temporal complexity of drift sedimentation and provide the first detailed proxy for Labrador Current flow since the last glacial maximum.

Comparison of Quaternary Glaciogenic Debris Flows with Blocky Mass-Transport Deposits in Orphan Basin, Offshore Eastern Canada

Quaternary deposits in southern Orphan Basin include complex mass transport deposits (MTD) comprising both glaciogenic debris flows (GDF) and blocky MTD. 3D seismic reflection data were used to highlight the difference between the two types of MTD. The main MTD in southern Orphan Basin were sourced from the slope off Trinity Trough in the west of the basin. On the Trinity Trough-mouth Fan, a succession of GDF was deposited above horizon B5, interpreted to date from Marine Isotope Stage (MIS) 12. Beyond the direct influence of Trinity Trough, MTD unit 2 below horizon B5 is confined within pre-existing channels, which are in approximately the same location as the modern Bonanza Channel and Sheridan Channel. Blocky MTD are characterized by linear and divergent basal grooves and chaotic internal facies. Dispersed blocks, less than 1 km2 in area, are commonly present within the blocky MTD on the southern Orphan slope. The tongue of the main Sheridan MTD is sharp-edged, with a series of closely spaced pressure ridges. 3D seismic data of GDFs show few features diagnostic of blocky MTD. Both stacked GDF lobes and channelized GDF are observed on Trinity Trough-mouth Fan.