Very large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland
Very large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland
Scottish Journal of Geology (November 2019) 55 (2): 155-165
- Antarctica
- Arctic region
- bedding plane irregularities
- bedrock
- Cenozoic
- clastic sediments
- deglaciation
- depositional environment
- Devensian
- erosion
- Europe
- flute casts
- glacial erosion
- glacial geology
- glaciation
- glaciers
- Great Britain
- Greenland
- Hebrides
- Highland region Scotland
- ice movement
- ice streams
- incised valleys
- Inner Hebrides
- Inverness-shire Scotland
- Isle of Skye
- landforms
- moraines
- Neoproterozoic
- Pleistocene
- Precambrian
- Proterozoic
- Quaternary
- Scotland
- scour
- sedimentary structures
- sediments
- till
- Torridonian
- United Kingdom
- upper Pleistocene
- upper Precambrian
- Western Europe
- Applecross Scotland
- Beinn Ghobhlach
We describe two large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland, and point out their resemblance to a number of landforms emerging from presently deglaciating areas of Greenland and Antarctica. We suggest that they all result from locally sourced sediment being deposited by local ice-flow, which was laterally confined by the margins of much larger adjacent glaciers or ice-streams. The NW Highlands features thus seem likely to be the result of processes active during the latter part of the Devensian Glaciation. One of these deposits, on the peninsula between Loch Broom and Little Loch Broom, is evidently sourced from the west-facing Coire Dearg of Beinn Ghobhlach, but was emplaced in a WNW direction rather than along the WSW fall-line. This suggests that the ice that emplaced it was confined by the margins of large glaciers then occupying the adjacent valleys of Loch Broom and Little Loch Broom. The second much larger and more prominent deposit, in Applecross, is composed of bouldery Torridonian sandstone till emplaced on to glacially scoured bedrock; the only feasible source location for this material is about 12 km distant, which requires that the deposit was carried by ice across the trough of Strath Maol Chalum and emplaced while active ice-streams confined it laterally to its present-day location. This, in turn, requires that ice lay in the Inner Sound between Applecross and Skye to an elevation 400-500 m above present-day sea-level. The Wester Ross Re-advance of 15-14 ka left a fragment of lateral moraine against the most easterly flute and buried the distal end of the flutes with hummocky moraine. We hypothesize that the fluted deposits reflect the locations of the ice-stream margins that constrained deposition of locally derived ice-transported sediment, rather than the flow-lines of the ice-stream itself.