Re -Interpretation Of 'Hummocky Moraine' In The Gaick, Scotland, As Erosional Remnants: Implications For Palaeoglacier Dynamics

Many glaciated valleys in Scotland contain distinctive, closely spaced ridges and mounds, which have been termed 'hummocky moraine'. The ridges and mounds are widely interpreted as ice-marginal moraines, constructed (luring active retreat of mainly temperate glaciers. However, hummocky terrain can form by various processes in glacial environments, and it may relate to a range of contrasting glaciodynamic regimes. Thus, detailed geomorphologic-al and seclimentological studies of hummocky surfaces in Scottish glaciated valleys are important for robust interpretations of former depositional environments and glacier dynamics. In this contribution, we examine irregularly shaped ridges and mounds that occur outside the limits of former Loch Lomond Readvancc ( Younger Dryas;-12D-11.7 ka) glaciers in the Gaick, Central Scotland. These ridges and mounds are intimately associated with series of sinuous channels, and their planform shape mimics the fon-n of the adjacent channels. Available exposures through ridges in one valley reveal that those particular ridges contain lacustrine, subglacial, and glaciofluvial sediments. The internal sedimentary architecture is not related to the surface morphology; thus, we interpret the irregularly shaped ridges and mounds as erosional remnants (or interfluves). Based on the forms and spatial arrangement of the associated channels, we suggest that the ridges and mounds were generated by a combination of ice-marginal and proglacial glaciofluvial incision of glaciogenic sediments. The evidence for glaciofluvial incision, rather than ice-marginal moraine formation, al pre-Loch Lomond Reaclvance glacier margins in the Gaick may reflect differences in glaciodynamic regimes and/or efficient debris delivery from the glader margins to the glaciofluvial systems. (C) 2021 The Geologists' Association. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).