Age and significance of mountain-top detritus

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    82 Citations (Scopus)

    Abstract

    In north-west Scotland, mountain-top detritus forms blockfields or diamicts, depending on lithology. Clast angularity, absence of grussification and transition to underlying rock imply formation by frost-wedging of bedrock. Age is constrained by trimlines and exposure dating of weathering zones. Mountain-top detritus is ubiquitous on nunataks that remained above the level of the last ice sheet, but occurs only on well-jointed rocks in areas exposed to periglacial conditions since ice-sheet downwastage and is absent from areas exposed to weathering only during the Holocene. Most secondary clay minerals are equally represented both above and below a trimline cut by the last ice sheet, indicating formation since deglaciation, though haematite and gibbsite are preferentially represented on former nunataks. The age and significance of mountain-top detritus are determined by lithology and glacial history. On well-jointed rocks, such detritus has developed within a few millennia of exposure to periglacial conditions. On massive lithologies, however, it has formed over much longer timescales on nunataks above the last and possibly earlier ice sheets. In north-east Scotland ancient (possibly pre-Pleistocene) regolith also appears to have survived under a cover of cold-based ice. Use of the distribution of mountain-top detritus in palaeoglaciological reconstructions therefore requires caution. (C) 1998 John Wiley & Sons, Ltd.

    Original languageEnglish
    Pages (from-to)327-345
    Number of pages19
    JournalPermafrost and Periglacial Processes
    Volume9
    Issue number4
    DOIs
    Publication statusPublished - Oct 1998

    Keywords

    • mountain-top detritus
    • blockfields
    • weathering
    • periglacial trimlines
    • weathering zones
    • clay minerals
    • cosmogenic isotope dating
    • LAST ICE-SHEET
    • NORTHWEST SCOTLAND
    • SOUTHERN NORWAY
    • HIGH PLATEAUS
    • GLACIATION
    • HIGHLANDS
    • ALTITUDE
    • NUNATAKS
    • GASPESIE
    • ICEFIELD

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