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 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 362.70-362.80

Multiple domains are present. Clasts range from small to large in size and sub-angular to sub-rounded in shape. The fine grained domain is dark brown with some lineations and organic material. The coarse grained domain is grey in colour and contains mainly lineations and rotation structures. Some comet structures can also be seen.

HG 421.50-421.60

Light brown sediment with clasts that range from small to large in size. The clast shape ranges from sub-angular to sub-rounded. Lineations and rotation structures are abundant in this sample. Edge-to-edge grain crushing is present as well. There are areas of light and dark sediment throughout the sample. A few comet structures can also be seen.

HG 87.30-87.35

Dark brown sediment with clasts ranging from small to medium in size. Clast shape ranges from angular to sub-rounded. Rotation structures and lineations are common throughout the sample. Comet structures and grain stacking/crushing can also be seen in minor amounts.

HG 168.50-168.60

Brown sediment with three main domains; two different fine grained domains and one coarse grained domain. The fine grained domains can be distinguished based on the abundance of organic material (darker). Both domains contain lineations. The coarse grained domain contains clasts ranging from small to medium in size and angular to rounded in shape. Rotation structures, lineations and comet structures can be seen in this domain. It also contains some fractured grains.

09CR 137-2.1

Brown sediment with clasts ranging from small to large. Clast shape ranges from angular to sub-rounded. Lineations and rotation structures are common. This sample also contains crushed grains, edge-to-edge grain crushing and grain stacking. Many comet structures can also be seen throughout the sample.

AI-2

Brown sediment with clasts ranging from small to large in size. Clast shape ranged from angular to rounded. Lineations and rotation structures can be seen throughout the sample. Rotation structures are common around medium and large sized clasts. Some comet structures , grain stacking, and crushed grains can also be seen in minor amounts. This sample also contains areas with clay and dark organic rich material.

WB-3b

Dark brown sediment with well dispersed clasts. The clasts range from small to large in size and sub-angular to sub-rounded in shape. The sample is abundant in rotation structures and lineations. It also contains comet structures and minor amounts of grain stacking.

11 PTA0010A

Greyish brown sediment with clasts ranging from small to large in size. Clast shape ranges from angular to rounded. Many grains in this sample are fractured. Rotation structures and lineations are the most common micro-structures that can be seen in this sample. Grain crushining, grain stacking, and comet structures can also be seen.

Mo04

Greyish brown sediment with clasts ranging from small to medium in size. Clast shape ranges from sub-angular to rounded. Lineations and rotation structures are common throughout the sample. Rotation structures were seen around all sized clasts. This sample also contained a few areas of edge-to-edge grain crushing as well as crushed grains. Minor amounts of comet structures can also be seen.

MoNo 140671

Greyish brown sediment with clasts ranging from small to medium in size. Clast shape ranges from sub-angular to rounded. Lineations and rotation structures can be seen scattered throughout the sample. Comet structures can also be seen in certain areas of the sample. Minor amounts of grain crushing and stacking can also be seen.

MoNo 140672

Brown sediment with clasts ranging from small to large in size. Clast shape ranges from sub-angular to sub-rounded. Many larger clasts appear fractured and/or weathered. Lineations and rotation structures can be commonly seen. Comet structures are also present. Minor amounts of grain crushing and stacking can also be seen.

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.