Shawn Goss

The Hamilton Spur is a large late Cenozoic sediment drift feature, that trends northeastward between 300 m and 3000 m water depth on the Labrador continental margin. The objective of this study is to understand the Quaternary development of this large deep water drift which formed by the southward flowing Labrador Current and Western Boundary Undercurrent reworking and depositing continental margin sediments. To gain a better understanding of the processes that directly influence the Hamilton Spur, 289 km of single channel air gun seismic reflection, Huntec subbottom data and three piston cores were examined. The study mapped a major near surface unconformity that marks the initiation of the Labrador Current, defined by the erosion of a pre-existing sediment drift. Overlying the unconformity, 5 key horizons were mapped indicating a southward migration of the Hamilton Spur. The northern flanks of the spur are subjected to intense current velocities and current reworking, with subsequent deposition on the southern flanks of the ridge where decreases in current velocities cause a loss of sediment suspension within the water column, evident in thickened units. Six seismic facies have been established on the Hamilton Spur indicating variations of depositional environmental over the spur depending on depth and location to current axis. Piston cores support the idea of current influenced deposition in which increased sediment thickness is observed. Cores contain 5 lithofacies, indicating changes in depositional patterns over the ridge The outer margin and upper slope (~300-1200 m) of the northern flanks are controlled mainly by the deeper Labrador Current component where clays and silty sediments are subjected to winnowing, leaving more coarse sands and lag deposits. The middle slope region (~1200 m) is considered to be unaltered by currents defined by a Azone of minimum motion@. The lower base and northern flanks (1200-3000 m) are subject to the intense axis of the Western Boundary Under Current, responsible for considerable reworking of bottom material and the presence of considerable amounts of sands, and minor traces of silts. Seismic reflection data and piston cores collected support the idea of southward flow of the Labrador Current and Western Boundary Undercurrent. Sedimentation processes such as mass transport deposits and glacial melt-water deposits followed the development of the unconformity. Under modern conditions, current intensity and sedimentation rates have decreased on the Spur, however the Hamilton Spur=s depocenter continues its southward migration.

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Pages: 76
Supervisor: David Mosher