Morphology and Significance of Transverse Ridges (De Geer Moraines) Adjacent to the Moray Firth,NE Scotland

Abstract

High-resolution NEXTMap digital surface models and aerial photographs are used to map suites of transverse ridges at Tarbat Ness and to the west of Elgin, along the margins of the Moray Firth in northeast Scotland. Based on their morphology, configuration and location, interpret these landforms as De Geer moraines which formed at or near former grounding line positions of the Moray Firth palaeo-ice stream. The Tarbat Ness De Geer moraines almost certainly formed at a marine margin. Reaching altitudes of 55 m above present OD, these landforms may provide one of the highest geomorphological indicators for former relative sea level in mainland Britain. Evidence from surrounding landforms and sediments suggest that the ridges formed between c. 15 000–18 000 cal yrs BP, indicating that a significant fall in relative sea level may have taken place prior to an ice margin re-advance in the Moray Firth, known as the Ardersier Oscillation.