Pattern of deglaciation of the last (Late Devensian) Scottish ice sheet: Evidence from ice‐marginal deposits in the Dee valley, Northeast Scotland

Abstract

Brown, 1. M. Pattern of deglaciation of the last (Late Devensian) Scottish ice sheet: evidence from ice-marginal deposits in the Dee valley, northeast Scotland lournaf ABSTRACT: The mode of deglaciation of the last Scottish ice sheet is assessed from evidence provided by geomorphological mapping and sedimentology. ice-marginal deposits in the Dee valley have a distinctive morphological expression and a characteristically varied sedimentology that strongly resembles those from subpolar glaciers. The deposits tend to occur in certain topographic situations which can be accounted for by compression of ice near the margin and formation of an ice-cored supraglacial land system. A series of recessional stages of the ice-front can be mapped demonstrating that active retreat occurred. However, additional evidence shows there was probably a thin marginal zone of stagnant ice. Recessional stages are inferred to be stillstands that are considered to be topographically controlled rather than related to climate. Development of the supraglacial land system during deglaciation suggests that the ice sheet had a polythermal basal regime with a cold-based margin. This implies that deglaciation took place in northeast Scotland while the climate remained cold, probably due to a precipitation deficit, which agrees well with chronostratigraphic data. J w r m I of Quaternary Science

Formalising an inversion methodology for reconstructing ice‐sheet retreat patterns from meltwater channels: application to the British Ice Sheet

“…British National Grid co-ordinates persists in modern literature (e.g. Brown, 1993;Russell, 1995). We feel it is a useful distinction, if only to exclude those lateral channels which should not be used to demarcate ice-margin positions.…”

Middle to Late Devensian glaciation of north‐east Scotland: implications for the north‐eastern quadrant of the last British–Irish ice sheet

“…There was probably a sequential south-westward 'un-zipping' down the North Sea coast of 'Strathmore' and 'East Grampian' ice during deglaciation (Simpson, 1955), possibly accompanied by a marine incursion up to about 30 m OD (Peacock, 1999). Minor readvances at Aberdeen, Dinnet and Aboyne are thought to have interrupted the general westward retreat of East Grampian ice (Jamieson, 1906;Bremner, 1931;Bremner, 1943;Synge, 1956;Sutherland and Gordon, 1993;Brown 1993Brown , 1994Evans et al, 2005). Important evidence for a minor, late-stage onshore readvance of Moray Firth ice occurs at St Fergus (Figure 6c), where raised marine deposits lying up to about 17 m OD have been deformed within a low ridge, probably a push moraine (Hall and Jarvis, 1989;Peacock, 1997).…”

The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain

“…The Aberdeen-Lammermuir Readvance (Synge, 1956;Sissons,1967aSissons, , 1981 was proposed to account for almost continuous assemblages of glacifluvial sands and gravels. In the Aberdeen area this is typified by a 3 km wide belt of ice-marginal deposits stretching across the lower Dee valley (Brown, 1993). Linear accumulations of glacifluvial deposits were mapped in the Aberdeen area by Synge (1963b) and associated with glacier margins during readvances (e.g.…”

“…Such features were previously assigned to a Dinnet Readvance by Bremner (1931a) and Synge (1956) and then reinterpreted as stagnation deposits by Sugden (1972, 1977), Sugden and Clapperton (1975) and Murdoch (1975). The most recent assessment of the ice-marginal deposits in the Dee Valley by Brown (1993) proposes a marginal supraglacial origin similar to the evolution of moraines on sub-polar glaciers. This explains their linearity and diverse sedimentology and indicates a series of glacier recessional stages.…”

“…The bracketing of other major landform assemblages in Scotland has proved difficult in the absence of good chronostratigraphic control. An age bracket for the ice-marginal landforms of the lower Dee Valley (Brown, 1993) is provided by a radiocarbon date of 12.6 ka BP on basal peat near Braemar and a minimum age of 15,370 years BP for onshore recession of ice on the coast of Aberdeenshire (Hall and Jarvis, 1989). The maximum age of the Ardersier Readvance in the Moray Firth (Merritt et al, 1995) is provided by the dating of the Errol Beds that were glacitectonized during ice overriding.…”