Thian Hundert

Strata on the western Scotian Slope provide a high resolution and continuous record of the late Quaternary glacial processes that took place in the region, as a case timing and behaviour of decaying marine ice sheets in response to climatic change. This study used three principal tools to study the western Scotian Slope; multibeam bathymetry, high-resolution reflection seismic profiles and piston core sediment samples.

Multibeam bathymetry showed glacial fluting and mega lineations on the outer western Scotian Shelf. The clarity and apparent freshness of these features suggest that they were of last glacial maximum (LGM) origin and likely correspond to till tongues observed in the seismic reflection profiles on the upper western Scotian Slope, indicating that ice flow reached the upper western Scotian Slope at LGM. Furthermore, the identification of a southward trending shear margin moraine originating on the east side of Browns Bank towards the shelf break indicates two different ice flow velocities existed on the western Scotian Shelf: faster flowing ice that produced the flow features in the topographical low between Browns Bank and Baccaro Bank and a slower moving ice mass over Browns Bank.

Four principal lithostratigraphic units were characterized from piston cores and high-resolution seismic reflection profiles. Unit 1 is dated as older than 17 ka and is characterized by the dominance of facies 1 (thinly laminated mud turbidites), associated with hyperpycnal turbidity flows generated from sediment-laden meltwater from a proximal ice margin on the upper slope. Unit 2 is confined to 17-16 ka and is distinguished by an increase in very fine sand, a shift in colour from grey to brown and the dominance of facies 3 (massive silty/sandy clay) and facies 4 (massive silty/sandy clay with ice rafted detritus). The high sedimentation rate and the dominance of facies 3 and 4 indicate that the sedimentation was principally from that of iceberg rafting meltwater plumes. The change in facies type from unit 1 suggests that the ice margin was no longer supplying sediment directly from the upper slope but that it had retreated onto the shelf. The increase in brown colour and the increase in sand on the slope also suggest that the shelf edge was exposed, allowing for the mixing meltwater plumes and reworking of seafloor sediments by oceanic waves and currents. This early ice retreat was limited to the areas of faster flowing ice, whereas areas of slower flowing ice retreated later. Unit 3 represents sedimentation between 16 and 14 ka and is characterized by similar facies to those of unit 2, but exhibits an alternation between a sandy brown facies 3 and redder finer grained facies 4. This pattern is interpreted to represent a further retreat of the ice sheet on the western shelf, such that the ice sheet no longer directly influenced the western Scotian Slope sedimentation. Rather, sediment was either transported by; 1) current reworking of outer shelf clastics, spilling it over onto the slope, producing the sandy brown units, or 2) melt-water plumes transporting redder sediment along the slope from the east. The capping melt-water beds "d" and H1 further confirm the along shore transport of material from the east. These beds are well dated in the literature (14 ka). They form the boundary between unit 3 and unit 4 and mark a transition to a slower sedimentation rate with less ice rafted detritus (IRD). The lower part of unit 4 is coarser and contains some IRD and brick red meltwater plume deposits, most common of which is "b". However after 10 ka there is little evidence of glacial influence on the western Scotian Slope.

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Supervisor: D. J. W. Piper