|John Merritt describing the Alturlie Gravels that formed|
from a retreating ice sheet.
To Moraine or not to MoraineAn optional day to start, organised by Martin Kirkbride and Adrian Hall, took us high into the Cairngorm Mountains to look at a newly defined moraine that represents the development of a Little Ice Age glacier in Coire an Lochain. Martin presented evidence for his interpretation of the moraine, with combination of geomorphology, cosmogenic dating and glacial modelling. Fortunately, his hypothesis managed to withstand the scrutiny of the party, even as the rain started to pour! Check out his paper.
Its main event time!
The following three days were the main field trip, which explored the glacial landscapes and features along the edge of the Moray Firth. We started off at Alturlie Point where we looked at deltaic deposits related to a retreating Moray Firth ice-stream. There was much debate regarding the presence of gravel in the deposit and whether these could possibly represent kettle hole deposits in the delta. Elsewhere quickly deposited gravels resulted in some very eye-catching soft-sediment load structures.
Following on from this we went on to the SSI site at Ardersier to look at world-class folding and soft-sediment deformation structures in the Ardersier Silts. Emrys Phillips guided us through these complex structures, showing the benefits of applying some structural geology knowledge to glaciology, a fantastic example of interdisciplinary collaboration in science. This spectacular site shows the power of a moving glacier and how it can deform sediments, representing a crumple zone in fore-front of the glacier.
|From L-R: Ball and pillow soft structures in the Ardesier Silts; Sandy inter-beds within the Alturlie Gravels.|
Seriously, this is a rock?
Day 2 and the impressive geology kept coming. We started by looking at the Old Red Sandstone. Upon arrival we find a “rock” that can be dug out with a spade. This remarkable change in character is due to the de-calcification of the rocks, making them a pale white colour, providing a very soft section. It’s the hydrofracturing that really captures the imagination of the group. The pressure and movement of the glacier above has resulted in high-pressured water causing fractures in the bedrock. The fractures are filled with clay and contains broken up pieces of the surrounding Old Red Sandstone.
|From L-R: The group exploring hydrofracture networks in the Old Red Sandstone, related to an overriding glacier;|
Decalcification and hydrofractures in the Old Red Sandstone.
Landscapes and deposits of the Findhorn Valley
The final day of the trip was spent in the stunning and picturesque Findhorn Valley. Incredibly, the valley has Devonian (420-360 Ma) aged deposits, suggesting that it was also a valley in the Devonian time. This was a natural point for Adrian Hall (also a BGS VRA) to jump in and give us an overview of ancient landscapes in the area. This resulted in a spirited debate on the uplift history of Scotland. Was the Scottish Highlands ever covered in Cretaceous-aged chalk? We certainly see them in the offshore area, but how far did this extend on-land? Watch this space for some very exciting science in the future!
The final section of the trip was in the river cliffs along the River Findhorn. The 15 m thick section exposed, represents glacial-meltwater draining from an ice-front resulting in small delta/fan pro-grading down the valley. The energy of the delta system was represented by metre sized rip-up blocks that are now entrained in the fluvial deposits. A more recently exposed section shows lacustrine rhythmites and spectacular photogenic climbing ripples that underlie the glacial delta deposits, representing older phases of the glacial delta/fan system.
Overall, a fascinating trip which provided an excellent opportunity to see some of the most interesting glacial features and deposits in Scotland. Most importantly the excursions created an environment for lively and enthusiastic debate. Many thanks to field trip leaders for organising a fantastic trip and I look forward to QRA/GLWG 2018 in sunny Iceland!