| Abstract |
This report provides an overview of field observations from a two day visit to an exposed trench section through the Ardersier Silts Formation that crop out in the moraine that forms the Lateglacial cliffline, near the village of Ardersier in the Highlands Region of north-east Scotland. This section is within the SSSI site for the contorted silts of Ardersier, which are exposed in a nearby cliff face. The trench section exposed nearly 10 m of interbedded silts, sands and gravels and occasional clay veins._x000D_
The trench section, which was continuous, was divided into upper, middle and lower portions for ease of description. The upper part of the section comprises a gravel and fine to medium-grained light brown to grey-coloured sand with lamination and occasional planar cross-bedding. This unconformably overlies a fine to medium-grained sand with planar cross bedding._x000D_
The middle part of the section comprises a fine-grained sand with well-developed multiple beds of sand showing parallel lamination, planar-crossbedding and minor reverse faulting. In addition, relatively small (1–5 cm thick) sub-horizontal to sub-vertical clay veins cut through the entire sequence._x000D_
The lower part of the section comprises a fine to medium-grained sand with massive clay veins and brecciation of the sand within the veins. The blocks of sand vary from centimetres to metres in size. The clay veins also vary in width from 2 cm to nearly 40 cm._x000D_
Throughout the section are well-preserved fluid oxidising pathways. These both follow bedding and are displaced across bedding, by small-scale faulting and by fluid migration fronts. They form complex anastomosing networks of staining and occasional concentrations of silt and clay. Generally, the oxidising fluids appear to have migrated along the clay veins and diffused into the surrounding sand._x000D_
Structural measurements from the largest and most prominent clay veins indicate that they are all of broadly similar dip and orientation. This may indicate that they all formed as a result of the same phase of fluid movement and glaciotectonic displacement that took place during the formation of the moraine. The upper portion of the newly exposed section, exhibits many of the features previously described from the sands exposed beneath the Baddock Till at the Hillhead Section, whereas the middle and lower parts resemble the sediments and structures that exposed within the Ardersier Silts Formation, beneath the Baddock Till, in the Jamieson's Pit section._x000D_
The well-exposed sedimentary structures within the sediments of the Ardersier Silts Formation are interpreted as a coastal shallow marine setting. The well-preserved hydrofracture network within the section demonstrates the diverse range of glacial deformation that occurred during deglaciation. It is likely that the hydrofracture network developed as consequence of ice-push and possibly glacial over-riding during the deglaciation of the Moray Firth ice-stream. |
