The last British Ice Sheet: A review of the evidence utilised in the ...

thereby demarcating the upper limits of the last ice sheet (e.g. Ballantyne, 1990; Ballantyne and McCarroll,
1995; McCarroll et al., 1995; Ballantyne, 1997; Ballantyne et al., 1997; McCarroll and Ballantyne, 2000).
Although alternative interpretations of periglacial trimlines as the former boundaries of ice sheet thermal
regimes persist (e.g. Kleman and Borgstrom, 1990), the increasing number of pre-LGM dates on blockfields
(e.g. Stone et al., 1998; Bowen et al., 2002) together with independent evidence of prolonged periods of
weathering, for example the occurrence of gibbsite (Ballantyne, 1994; Dahl et al., 1996), appear to be
confirming the existence of full glacial unglaciated enclaves. In the absence of large numbers of sites with
pre-LGM/sub-till dates, the continued mapping and dating of palaeo-nunataks will provide the most
comprehensively dated upper limits of former glaciation in the British Isles.
3.2. The British Ice Sheet maximum limits
The greatest paucity of data regarding the LGM British Ice Sheet lies in the realm of dating maximum limits
in lowlands and offshore areas. The most significant dates on the LGM are from the following regions:
(a) the northern North Sea where Sejrup et al. (1994) propose coalescent Scandinavian and British ice based
upon a till dated 22 ka–29 ka BP. This was followed by a readvance, correlated with the Dimlington
Stadial, between 19 ka and 15 ka BP;
(b) the NW continental shelf where a 27.3 ka BP maximum age for the LGM comes from the Isle of Lewis
and glacimarine sediments distal to morainal banks south of St Kilda date to 22.5 ka BP;
(c) on Holderness where maximum ages for ice advance are 18.5 ka BP (Penny et al., 1969) and 17.5 ka BP
(Wintle and Catt, 1985) but an age as recent as 14 ka has been proposed (Peacock, 1997);
(d) on the Lincolnshire Wolds, Lake Humber I is dated at 21.8 ka BP (Gaunt, 1974, 1976, 1981);
(e) in North Wales, the glaciation of the Lleyn Peninsula occurred sometime after 29 ka BP and a sub-till age
of 18 ka BP in the Vale of Clwyd predates either the LGM or a later readvance (Rowlands, 1971; Bowen,
1974);
(f) in south Wales a maximum age on LGM glaciation of the west side of the Gower is 17 ka BP (Bowen et
al., 1986; Bowen and Sykes, 1988), and a 36Cl age of 23.2 ka was obtained by Bowen et al. (2002) on the
Arthur’s Stone erratic boulder on the southcentral Gower;
(g) in the west Midlands, glacial sediments at the Four Ashes type site post date 30 ka BP (Morgan, 1973);
(h) on the Scilly Isles a maximum age for glacial advance is 21 ka BP (Scourse, 1986, 1987, 1991a,b);
(i) in Northern Ireland a maximum age for the advance of Scottish Highland ice is 24.1 ka BP. It is clear that
significantly more geochronological control is required in order to elucidate the timing of LGM ice sheet
advance, oscillations and retreat history in Britain. Although cosmogenic radionuclide dating is
providing more success in demarcating the upper limits of the ice sheet, considerable problems remain in
the lowland and offshore locations of ice sheet termini due to the lack of appropriate datable materials.
This geochronological problem applies also to sedimentlandform associations deposited during the
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