Lateglacial ice extent and deglaciation of Loch Hourn, western Scotland

Abstract

Synopsis Loch Hourn is a 21 km-long fjord on the west coast of Scotland. A multibeam survey of the outer Loch Hourn basin extending into the adjacent Sound of Sleat reveals a series of moraines beyond the fjord mouth relating to the Scottish ice cap during the Lateglacial period ( c . 15–11 cal ka BP). The outermost moraine is located in the Sound of Sleat, 3.5 km beyond the currently accepted limit of Younger Dryas Stadial glaciation in the loch. Sediment cores from the main outer basin of the fjord sample four lithological units: a coarse-grained basal sand, interpreted as an ice-proximal deposit; finely laminated silts containing occasional clasts, interpreted as a distal glaciomarine unit deposited through pelagic settling from glacial meltwater and turbidity current activity; a poorly sorted mixture of muddy sands containing convolute bedding and flame structures, interpreted as slumped glacigenic material; and poorly sorted, bioturbated marine muds with mollusc shells ( Arctica islandica ) which yielded a basal radiocarbon date of 11.2 cal ka BP, indicating that open-marine conditions typical of the Holocene were established in the fjord by this time.