Box 68 Preservation Of Landforms And Sediments Beneath Coldbased Ice Sheets

In cold-based areas beneath ice sheets, where there is little or no basal melt-water, there is little or no glacier sliding. As a result, the basal layers of the ice sheet are frozen to the bed and the processes of glacial erosion are severely limited. This means that in these areas it is possible for older, non-glacial landforms to survive ice-sheet overriding. Evidence now exists for the preservation of a range of different landforms and sediments beneath former ice sheets. Initially these interpretations of landscape preservation were based solely on geomorphological evidence such as the survival of upland landscape elements, for example plateau surfaces (Clarhall and Kleman, 1999). More recently, however, cosmogenic radionuclide evidence (Box 6.10) has been used to provide quantitative data on other landforms, which indicates that very old landscape elements can survive beneath ice sheets. Landforms dated in this way include upland tors (Stroeven et al., 2002; Briner et al., 2003) and moraines (Fabel et al., 2006), as well as also lowland glacial features such as glaciomarine deltas (Davis et al., 2006) and sediments in lake basins (Briner et al., 2007). The photograph below shows a tor with a perched erratic in the Canadian Arctic from Briner et al. (2003).

Sources: Briner, J.P., Miller, G.H., Davis, P.T., et al. (2003) Last glacial maximum ice sheet dynamics in arctic Canada inferred from young erratics perched on ancient tors. Quaternary science reviews, 22,437-44. Briner, J.P., Axford, Y., Forman, S.L., et al. (2007) Multiple generations of interglacial lake sediment preserved beneath the Laurentide ice sheet. Geology, 35, 887-90. Clarhall, A. and Kleman, J. (1999) Distribution and glaciological implications of relict surfaces on the Ultevis Plateau, northwestern Sweden. Annals of glaciology, 28, 202-8. Davis, P.T., Briner, J.P., Coulthard, R.D., et al. (2006) Preservation of Arctic landscapes overridden by cold-based ice sheets.

Quaternary research, 65, 156-63. Fabel, D., Fink, D., Fredin, O., et al. (2006) Exposure ages from relict lateral moraines overridden by the Fennoscandian ice sheet. Quaternary research, 65, 136-46. Phillips, W.M., Hall, A.M., Mottram, R., et al. (2006) Cosmogenic Be-10 and Al-26 exposure ages of tors and erratics, Cairngorm Mountains, Scotland: timescales for the development of a classic landscape of selective linear glacial erosion. Geomorphology, 73, 222-45. Stroeven, A.P., Fabel, D., Hattestrand, C. and Harbor, J. (2002) A relict landscape in the centre of Fennoscandian glaciation: cosmogenic radionuclide evidence of tors preserved through multiple glacial cycles. Geomorphology, 44,145-54. [Photograph: J. Briner]

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