Periglacial trimlines, former nunataks and the altitude of the last ice sheet in Wester Ross, northwest Scotland

Ballantyne, Colin K.; McCarroll, Danny; Nesje, Atle; Dahl, Svein Olaf

doi:10.1002/(sici)1099-1417(199705/06)12:3<225::aid-jqs302>3.0.co;2-a

Cited by 48 publications

(25 citation statements)

References 42 publications

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“…This conclusion calls into question interpretation of trimline evidence in NW Scotland as representing the upper limit of the LGM ice sheet (McCarroll et al 1995;Ballantyne et al 1997Ballantyne et al , 1998. In terms of geomorphology, clay-fraction mineralogy and exposure age, the mountains of NW Scotland exhibit similar contrasts between glacially eroded lower slopes and blockfield-covered summits to those of Caithness and F.…”

Section: Altitude Of the Last Ice Sheetmentioning

confidence: 99%

The altitude of the last ice sheet in Caithness and east Sutherland, northern Scotland

Ballantyne

Hall

2008

SJG

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SynopsisOn the mountains of southern Caithness and east Sutherland, geomorphological evidence for the upper limit of glacial erosion implies that, at the last glacial maximum (LGM), warm-based erosive ice extended up to altitudes of 410-600 m. Above the upper limit of glacial erosion is a cover of frost-weathered detritus, with tors on conglomerate bedrock. Kaolinite and gibbsite in soils on such terrain imply that it escaped significant glacial erosion at the LGM. This is confirmed by cosmogenic 10 Be exposure ages of (>) 146.6 15.1 ka and (>) 178.2 18.1 ka obtained for summit tors; sites below the upper limit of glacial erosion yielded deglacial ages of 16.6 2.1 to 18.5 2.4 ka. It is unlikely that glacially unmodified summits represent LGM nunataks, as the implied ice thickness is inconsistent with an ice sheet that extended across high ground on Orkney onto the Atlantic shelf; under conservative assumptions at least 70 m of ice must have covered the highest ground in southern Caithness at the LGM. We infer that the absence of evidence for glacial erosion on some summits and plateaux reflects cover by cold-based ice, frozen to the underlying substrate, that preserved the underlying tors and blockfields. This inference calls into question the use of similar evidence in NW Scotland to identify the maximum altitude of the last ice sheet.

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Section: Altitude Of the Last Ice Sheetmentioning

confidence: 99%

The altitude of the last ice sheet in Caithness and east Sutherland, northern Scotland

Ballantyne

Hall

2008

SJG

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“…Additionally, the higher hard IRM median value for abovetrimline sites may reflect spalling of fine-grained haematite fragments from the coatings of sandstone grains, thus enriching the concentration of high-coercivity minerals in the <63 µm fraction. Significantly, X-ray diffraction analyses detected haematite in the clay fraction of 14 (88%) of the above-trimline samples analysed, but in only one (11%) of the below-trimline samples (see Table 2 in Ballantyne et al, 1997).…”

Section: Discussionmentioning

confidence: 99%

Use of environmental magnetic measurements to validate the vertical extent of ice masses at the Last Glacial Maximum

Walden

Ballantyne

2002

J Quaternary Science

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Analysis of soil samples from above and below trimlines representing the upper limit of glacial erosion at the Last Glacial Maximum demonstrates that soils with prolonged weathering histories above such trimlines yield significantly different mineral magnetic signatures from soils below trimlines. The nature of the contrast is conditioned by lithology. Basalt soils above the trimline yield significantly higher values of concentration-dependent magnetic parameters (χ , χ arm , IRM 3T , soft IRM and hard IRM) than those below the trimline, due probably to transformation of nonmagnetic iron-bearing minerals into magnetic forms. Conversely, for sandstone soils most magnetic parameters yield significantly lower values for above-trimline samples, probably reflecting loss of ferrimagnetic minerals by dissolution and oxidation to aniferrimagnetic forms. These significant contrasts represent a new approach to validating high-level weathering limits as periglacial trimlines cut at the Last Glacial Maximum.

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“…The geology of the Western Red Hills is dominated by granitic intrusions (Bell and Harris, 1986), and the principal lithologies in Glen Docherty and Drumochter are micaschists (Harris and Johnson, 1991;Johnson, 1991). With the exception of the highest summits on Skye and in Wester Ross, the three sites were all submerged beneath the Late Devensian ice sheet (Ballantyne et al, 1987;Dahl et al, 1996;Ballantyne et al, 1997), and lie within the limits of the Loch Lomond Stade readvance (Sissons, 1974;Ballantyne, 1989;Bennett and Boulton, 1993;Bennett, 1994).…”

Section: The Field Sitesmentioning

confidence: 99%

Holocene reworking of drift-mantled hillslopes in the Scottish Highlands

Curry

2000

J. Quaternary Sci.

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Periglacial trimlines, former nunataks and the altitude of the last ice sheet in Wester Ross, northwest Scotland

Cited by 48 publications

References 42 publications

The altitude of the last ice sheet in Caithness and east Sutherland, northern Scotland

The altitude of the last ice sheet in Caithness and east Sutherland, northern Scotland

Use of environmental magnetic measurements to validate the vertical extent of ice masses at the Last Glacial Maximum

Holocene reworking of drift-mantled hillslopes in the Scottish Highlands

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