Determining rotational direction of rotation structures using prolate shaped grains within till

Micromorphology is used to analyze a wide range of sediments. Many microstructures have, as yet, not been analyzed. Rotation structures are the least understood of microstructures: their origin and development forms the basis of this thesis. Direction of rotational movement helps understand formative deformational and depositional processes. Twenty-eight rotation structures were analyzed through two methods of data extraction: (a) angle of grain rotation measured from Nikon NIS software, and (b) visual analyses of grain orientation, neighbouring grainstacks, lineations, and obstructions. Data indicates antithetic rotation is promoted by lubrication, accounting for 79% of counter-clockwise rotation structures while 21 % had clockwise rotation. Rotation structures are formed due to velocity gradients in sediment. Subglacial sediments are sheared due to overlying ice mass stresses. The grains in the sediment are differentially deformed. Research suggests rotation structures are formed under ductile conditions under low shear, low water content, and grain numbers inducing grain-to-grain interaction.

HG 186.15-186.25 Thin Section

Coarse grained sample with multiple fine grained domains. Clasts range from small to medium and sub-angular to sub-rounded. Mainly contains grain crushing (with grains crushed into one another) and short distance lineations. A few rotation structures are seen and fine grained sand domains can also be seen.

HG 186.80-186.85 Thin section

A coarse grained sample with clay rich domains. Grains range from small to medium and are sub-angular. Rotation structures can be seen around sub-rounded clasts. Lineations can be seen throughout the image, mainly short distance lineations. Small comet structures can also be seen throughout the images.

HG 186.9-187.0 D.E.

Coarse grained sediment with a few fine grained matrices. Brown sediment with small to medium sized clasts. Clasts range from sub-angular to sub-rounded. Organic material present. It contains rotation structures throughout as well as edge-to-edge grain crushing. Fine grained clay domains are present and lineations can also be seen. Minor amounts of grain stacking can also be seen.

HG 216.35-216.45

Brown, coarse grained sample. Clasts range from small to medium in size and sub-angular to angular. Patched of clay rich domains can be seen throughout the sample. Rotation with and without a central grain can be seen throughout the sample. Edge-to-edge grain crushing and grain stacking can be seen throughout the sample.

HG 222.70-222.80 Thin Section

Coarse brown sediment with clasts ranging from small to medium. Clasts are sub-angular to sub-rounded. Rotation structures can be seen throughout the image. Multiple rotations can be seen around single clasts. Minor amounts of comet structures and grain stacking can also be seen.

HG 230.75-230.85 Thin Section

Coarse grained sediment with fine grained domains, clay material, rotation structures and lineations. Clasts range from sub-angular to sub-rounded. Mainly brown sediment with darker patches of brown throughout. Major amounts of grain crushing can be seen in the coarse grained material.

HG 238.80-238.90 Thin Section

Dark brown sediment with clasts ranging from small to medium in size and sub-angular to angular. Contains lineations and grain stacking throughout the sample. Rotation and comet structures can also be seen. Rotation structures can be seen around mainly the sub-angular clasts. Patches of clay can also be seen throughout the sample.

HG 240.0-240.10 Thin Section

Dark brown sediment with sub-angular to rounded clasts. Contained areas of darker clay material. Contains rotation structures, mainly around rounded clasts. One side of the sample had significantly larger clasts than the other. Two different domains can be seen in this sample; a fine grained domain and a coarse grained domain.

HG 244.40-244.50-A Thin Section

Dark brown sediment with sub-angular to sub-rounded clasts. Rotation structures and lineations are common. Clasts ranging from small to large in size. Many large grains are fractured. Minor amounts of grain stacking and crushing can be seen. A few clay and organic rich domains can be seen.

HG 244.40-244.55-B Thin Section

Coarse grained sample with sub-angular to sub-rounded clasts ranging from small-large in size. Rotation structures, grain crushing and lineations were seen throughout the sample.

HG 246.30-246.45 Thin Section

Generally coarse grained, with a few different fine grained domains. Clasts range from small to large, ranging from sub-angular to sub-rounded in shape. Domain boundaries are clear, and the sample also contains rotation structures and lineations.

HG 249.40-249.55 Thin Section

Coarse grained sample with clasts ranging from small to medium. Clast shape ranges from angular to sub-angular. Lineations and rotation structures seen. Clay material and fine grained domains (darker colour) also seen.

HG 253.60-253.70

Coarse grained sample, with generally medium sized clasts. Clasts were sub-angular to sub-rounded. Many rotation structures, as well as large amounts edge-to-edge grain crushing are also present.

HG 264.30-264.45

Coarse grained sample with clasts that range from small to large in size. The clast shape ranges from angular to rounded, and many grains are fractured. Grain crushing is present in large amounts. This includes edge-to-edge crushing as well as grains that are crushed into one another. Rotation structures are also common among the clasts that are sub-rounded to rounded. Areas of finer sediment can also be seen.