The Quaternary deposits and landforms of Scotland and the neighbouring shelves: A review

Abstract

A thick sequence of Quaternary sediments (up to 1000 m) has been deposited in the North Sea Basin and perhaps five major glacial episodes, the first occurring prior to ca. 1.8–2.1 Ma BP and the last during the Late Devensian, can be recognised. Between the glacial events periods of low salinity arctic marine or glacio-marine sedimentation have been dominant although episodes of ameliorated climate when North Atlantic Drift waters had access to the North Sea have been identified. A number of horizons in separate boreholes have been correlated with the last interglacial (oxygen isotope stage 5e) and a sequence of water mass movements around the Scottish coasts can be reconstructed for the last ca. 125 ka. On land, sequences of Quaternary deposits relating to several glacial and non-glacial (terrestrial and marine) events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved. In particular, North-East Scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions. Evidence from the Outer Hebrides, North-East Scotland and the North Sea Basin indicates that the Late Devensian Scottish ice sheet had a rather restricted extent, only reaching a short distance offshore along much of the east and west coasts. At this time ice free areas existed in North-East Scotland, on the Isle of Lewis and, probably, in Caithness and Orkney, whilst part of the outer shelf around St Kilda was dry land. A marine embayment extended down the east coast of Scotland between the Scottish and Scandinavian ice sheets and independent ice caps existed on the Outer Hebrides and probably on Shetland. Deglaciation of the greater part of the country took place prior to ca. 13 ka BP whilst the climate was still very cold. The ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations. A number of retreat stages or minor readvances occurred during the general deglaciation. The Firth of Clyde was one of the last areas outside the Highlands to be deglaciated and this occurred in a rapid, possibly catastrophic, fashion shortly prior to ca. 13 ka BP. Despite the mild climate at the start of the Lateglacial Interstadial it is not known if there was complete deglaciation prior to the Loch Lomond Readvance. The Readvance glaciers, however, may have started to advance during the latter part of the Interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions. The Loch Lomond Readvance maximum can only be dated to some time after ca. 10.9 ka BP and it is likely that final ice free conditions were not achieved until the earliest Holocene.