Age and significance of mountain-top detritus

• Main Author: Ballantyne, Colin Kerr
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1998
• Subjects: 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; Norway; Ice Sheet; Permafrost and Periglacial Processes
• Online Access: https://research-portal.st-andrews.ac.uk/en/researchoutput/age-and-significance-of-mountaintop-detritus(8ee1b78d-8e28-4dec-bc7f-9ca9cc2ec945).html; https://doi.org/10.1002/(SICI)1099-1530(199810/12)9:4%3C327::AID-PPP298%3E3.3.CO;2-0; http://www.scopus.com/inward/record.url?scp=0032421874&partnerID=8YFLogxK

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.