Deglaciation and the terraces of the River Dee, Scotland

The terraces of the River Dee record the postglacial history of northeast Scotland. LiDAR data provide high resolution imaging of the geomorphic features, which, combined with field observations and borehole data has allowed the mapping of 112 km of the river valley. The lower river terraces exhibit meandering bedforms, likely formed in the Holocene. The upper terraces correspond to glacial outwash plains, back-stepping towards the west. These braided outwash plains are near-parallel to the riverbed in their distal, downstream sections, but terrace surfaces increase in slope upstream towards the west. Their upstream termination likely represents a stillstand point of the glacier. Two rock basins, at Ballater and at Braemar, each lie upstream of a wedge of ice-contact and distal outwash deposits, and may have marked ephemeral proglacial lakes, filled by lacustrine delta sediments. At least five separate flood deposits have also been identified, attesting to very high energy flooding events ( jökulhlaups ?) during the Lateglacial and potentially into the Younger Dryas. A model for punctuated glacial retreat in the Dee valley is developed. The evolution of the terraces provides a framework for understanding the paleoenvironment during early human activity in northeast Scotland. Most Mesolithic material is associated with the Lateglacial distal outwash, which would have been elevated terraces cut by a single meandering channel during the Holocene.