Micromorphology of ice keel scour in pebbly sandy mud and fine-grained sands: Scarborough Bluffs, Ontario, Canada

摘要

The keels of icebergs and ice-pressure ridges plough through unconsolidated sea/lake sediments gouging out long grooves known as ice keel scour marks. Although the surface and (more recently) subsurface morphology of scours are well-documented, little is known of the effect of grain size on the detectability, style and intensity of sub-scour deformation. This investigation macroscopically and microscopically (two-dimensional thin sections) examines suspected ice keel scour in: (i) glaciolacustrine pebbly sandy mud and (ii) fine-grained sands at Scarborough Bluffs, Ontario, Canada. In this investigation, there is an almost identical suite of deformation structures (individual structures and overprinted structural patterns) to those identified in iceberg-scoured clays from former Glacial Lake Agassiz (Manitoba, Canada); this confirms that deformation in the pebbly sandy mud and fine-grained sands at Scarborough Bluffs is likely to be indicative of ice keel scour. Discrete differences in the detectability, style and intensity of deformation between the Scarborough Bluffs and Glacial Lake Agassiz sediments are probably a function of grain size in response to ice keel scour. This research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes. This information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes. It also demonstrates the potential value of micromorphology where, for example, the study of cores is necessary.