CALCULATING QUATERNARY GLACIAL EROSION RATES IN NORTHEAST SCOTLAND

Northeast Scotland is an area exhibiting selective erosion by Quaterna ry ice sheets. In this area both glacial and preglacial landforms exis t in close proximity. The depths of erosion which this modification re presents are calculated on the assumption of various depths of preglac ial weathering. A depth of erosion of between 34 and 62 m per unit are a is indicated. Calculated rates of erosion are 0.021 mm a(-1) for the entire 2.3 m.y. of the Quaternary, and between 0.1 and 0.5 mm a(-1) o n the assumption that glacial conditions existed in this area for 500, 000 years and 100,000 years, respectively. These figures are compared to the offshore sedimentary record in the adjacent west-central North Sea. The volume of sediment deposited offshore is equivalent to a dept h of erosion of 195 m per unit area, yielding an average erosion rate of 0.085 mm a(-1) over the entire Quaternary. Rates of erosion were lo w in the preglacial Pliocene (0.049 mm a(-1)) and early Quaternary (0. 063 mm a(-1)), The expansion of ice sheets across the area in the midd le Quaternary was associated with a sharp increase in the rates of ero sion (> 0.13 mm a(-1)) but the last (late Devensian) ice sheet in the area was less erosive (< 0.095 mm a(-1)). The estimated rates of erosi on represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onshore geomorphological reconstruction.