Reply to the discussion by Dawson on ‘Late Devensian palaeoenvironmental changes in the sea area adjacent to Islay, SW Scotland: implications for the deglacial history of the island’ Peacock (2008), Scottish Journal of Geology , 44, 183–190

Abstract

J.D. Peacock replies : I am aware of the considerable contribution that Prof. Dawson and his co-workers have made to the elucidation of the Late Quaternary history of Islay, but I doubt that the evidence for their hypothesis, that the western part of the island and the Mull of Oa were ice-free during the Dimlington Stadial (DS), is sufficiently robust to refute the ‘conventional’ view that Islay lay within the Last Glacial Maximum (LGM) (22–26 ka bp). 1. The idea that the high-level glaciomarine deposits in the Rhinns (up to 80 m above OD) antedate the LGM is based chiefly on the three luminescence dates referred to by Dawson. The muds from which the dated samples were collected were presumably deposited from turbid meltwaters in which the rapid rate of deposition in a marine environment would have been accelerated by flocculation of the particles. Thus opportunities for ‘resetting the clock’ by sunlight would have been extremely limited, and for this reason alone the dates are suspect, and likely to be much too high. Moreover, recent improvements in dating of muddy sediments have resulted in much lower ages compared to those published earlier (e.g. Duller 2006). There is thus good reason to believe that redating the Islay muds would provide much lower ages. 2. The intensity of frost shattering and weathering in Islay as a whole is low, and similar to that within the LGM elsewhere in Scotland. In the Rhinns the bare bedrock surfaces above the level of the glaciomarine …