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Gibbsitic soils on former nunataks: implications for ice sheet reconstruction
Author(s) -
Ballantyne Colin K.
Publication year - 1994
Publication title -
journal of quaternary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.142
H-Index - 94
eISSN - 1099-1417
pISSN - 0267-8179
DOI - 10.1002/jqs.3390090107
Subject(s) - gibbsite , geology , escarpment , bedrock , regolith , soil water , weathering , frost weathering , ice sheet , geomorphology , geochemistry , soil science , kaolinite , astrobiology , physics
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.