A terrestrial ice-contact fan at Seathwaite in Borrowdale: characteristics and significance.

Peter Wilson, Alan Smith

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    Abstract

    An exposure in hummocky moraine of Loch Lomond Stadial age (12.9-11.7 ka BP) at Seathwaite in Borrowdale displays sedimentological and structural evidence suggesting development as a terrestrial ice-contact fan. The sediments display a tri-partite structure: a basal diamicton (Dmm) is overlain by down-valley dipping (~25°) sediments dominated by beds of silts and clays (Fm), sand (Sm), and gravel (Gms, Gm, Gfu), that are in turn overlain by a diamicton (Dmm) that is less compact than that at the base of the exposure. The basal diamicton is interpreted as a sub-glacial traction till and the overlying inclined sediments are regarded as a stack of interbedded mass-flow and meltwater sorted units derived from the supraglacial and englacial debris of the ice margin of the retreating glacier. The upper diamicton is most likely a flow till - a product of glacigenic debris flow. An absence of glaciotectonic deformation structures indicates that buried ice bodies were not present within or below the accumulating sediments, and that the glacier did not readvance into the fan. The fan is an example of the basic form and structure of such features with the implication that the ice margin was temporarily stable, enabling the fan to develop, before undergoing further retreat. The exposed sediments represent the first record of a terrestrial ice-contact fan in the UK outwith the Highlands of Scotland.
    Original languageEnglish
    Pages (from-to)41-49
    Number of pages9
    JournalThe Cumberland Geologist
    Volume4
    Publication statusPublished (in print/issue) - 21 Mar 2024

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