Sedimentary evidence for the formation mechanism of the Armoy moraine and late Devensian glacial events in the north of Ireland

Abstract

AbstractThe internal sedimentology of the Armoy moraine, which marks a late Devensian (Weichselian) incursion of Scottish ice into the north of Ireland, is described from a temporary exposure near Armoy village. The exposure (up to 30 m long, 10 m high) comprises folded gravel beds, massive clay grading up to pebbly diamicton, massive gravel, overfolded and deformed sand, and a gravel and massive diamicton cover. These sediments overlie glacially smoothed basalt bedrock. The sediment succession records the interaction of near‐touching Scottish and Irish ice margins, and the formation, infilling and drainage of an ice‐supported proglacial lake. Scottish ice likely advanced into the north of Ireland by a short‐lived glacier surge during the Killard Point Stadial (coeval with Heinrich Event 1 at 14.5 14C ka BP), forming the Armoy moraine at its maximum extent. The presence of rafted sediment blocks within the moraine suggests ice‐marginal thrusting and deformation of proglacial sands, and syntectonic resedimentation into low points on the sediment surface. Asynchroneity between Scottish and Irish ice‐marginal fluctuations may reflect differing responses to climate forcing during the Killard Point Stadial, or the effects of local factors such as substrate type and basal ice thermal regime. Copyright © 2004 John Wiley & Sons, Ltd.