Sedimentation in an ice-contact subaqueous setting: The mid-Pleistocene ‘North Sea Drifts’ of Norfolk, U.K.

Abstract

In East Anglia, the mid-Pleistocene ‘North Sea Drifts’ extend over some 1500 km 2 of the coastal zone of North Norfolk. They are the oldest Pleistocene glacial sequences exposed in Britain, deposited during the Anglian Glaciation (ca. 450 ka BP?). Laminated and stratified pebbly mud (diamict) facies of the North Sea Drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin. In this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body. Laminated, stratified, and massive diamict facies were deposited by the ‘rain-out’ of fine-grained sediment from suspension and coarse debris from floating ice, combined with downslope sediment gravity flow. Intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east, away from a major ice marginal moraine ridge (The Cromer Ridge). Exposures at Cromer show bulldozed ice-contact subaqueous sediments and ice-thrust chalk rafts. A fall in water-level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan-shaped ‘sag basins’ with diapiric structures at their margins. Comparable sedimentary sequences are exposed elsewhere around the southern North Sea Basin; a glaciomarine setting in response to glacio-isostatic depression around the Anglian ice sheet is suggested.