Gibbsitic soils on former nunataks: implications for ice sheet reconstruction

• Published in: Journal of Quaternary Science
• Main Author: Ballantyne, Colin K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1994
• Subjects: Ice Sheet
• Online Access: http://dx.doi.org/10.1002/jqs.3390090107; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjqs.3390090107; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jqs.3390090107

Abstract X‐ray diffraction analyses of soils above and below a periglacial trimline developed across the basalts of the Trotternish Escarpment (Isle of Skye, Scotland) demonstrate that gibbsite is restricted to soils above the trimline. This suggests that the gibbsite is a relict of pre‐Late Devensian weathering, and that the trimline did not develop after the last ice sheet achieved its maximum thickness. The sharpness of the boundary between frost‐weathered regolith and gibbsitic soils upslope and ice‐scoured bedrock associated with gibbsite‐free soils downslope suggests that the trimline represents the altitude of the last ice sheet at its maximum thickness rather than a former boundary between passive cold‐based ice and erosive warm‐based ice. These findings illustrate how identification of high‐level periglacial trimlines and associated contrasts in clay mineralogy provide a means for constraining reconstructions of the form of the last ice sheets.