Glacial erosion of the Wash and Fen basin and the deposition of the chalky till of eastern England

Abstract

It is widely accepted that the low-lying area of eastern England comprising the Wash and the Fens was excavated by the Anglian ice sheet. Moving first from the northwest and then from the north, the ice moved rapidly across the deformable bed on the Jurassic mudrocks and rode up over the Chalk escarpment, eroding the scarp face and setting back the lowered escarpment by several kilometres. The eroded material was deposited beyond the basin as the Chalky till of the southeast Midlands and East Anglia. In this paper reconstruction of the form of the preglacial landscape of the Jurassic and Cretaceous outcrops allows estimation of the excavated volume of both mudrock (312 km 3) and of chalk (243 km 3), a total of about 555 km 3. This volume, and the lithological mix, matches closely the reconstructed volume (estimate 363 km 3) of the now-dissected chalky till around the margins of the glacial lobe. The amount of erosion achieved by the Anglian ice sheet amounts to 3–4000 Bubnoffs (B) — i.e. mm ka −1, even if we allow 20 ka for a complex glaciation; this far exceeds rates of erosion recorded anywhere with the British Isles today: Even if averaged over the 440,000 yr since that event the rate is 167 B, far greater than the erosion achieved on similar rocks within the adjacent unglaciated Thames basin, estimated at 45 B.