Late Devensian glaciation, ice-dammed lake and river diversion, Stiffkey, north Norfolk, England

Abstract

SUMMARY A sequence of disturbed and undisturbed samples from a borehole drilled at Warham, near Stiffkey in north Norfolk, is described and sub-divided into three lithofacies on the basis of sedimentary structures, particle size distribution, calcium carbonate content, selected heavy mineral composition and indicator lithologies. These properties are used to determine the environment of deposition and establish correlation with glaciogenic deposits elsewhere. The basal sands and gravels (Lithofacies A) overlie the Chalk bedrock and are interpreted as having formed by a braided River Stiffkey that flowed northward through the site in pre-Late Devensian periglacial conditions. Lithofacies B consists of >8 m of laminated sands, silts and clays that were formed in a proglacial lake created by the obstruction of the River Stiffkey when the Late Devensian (Dimlington Stadial) glaciation reached the north Norfolk coast. These sediments are covered by gravelly sands (Lithofacies C), which were deposited as an ice-marginal river deposit as part of the Late Devensian end moraine-ridge complex. Finally, the lake drained and the sediments were dissected as the diverted River Stiffkey adopted a new course to the north-east and the lower, incised section of the present Stiffkey valley was formed.