East Anglia and adjoining areas - North Norfolk

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The base of the Chalk in the cliffs at Hunstanton, it rests on a layer of bright red sediment known as locally as the ‘Red Chalk’. P210683.

North Norfolk can broadly be equated with an area north of a line drawn from Kings Lynn through Norwich to Great Yarmouth; the other principal towns in this area include Hunstanton, Fakenham, Aylsham, North Walsham and Cromer. The coastline here is dominated by low cliffs (Plate P210683) with intervening stretches of sand spits, marshes and dunes.

Sedimentary bedrock[edit]

In this area there is a thick sequence of sedimentary bedrock layers which exceeds 1000 m in total between Cromer and Great Yarmouth in north-east Norfolk. As a result, the top of the underlying basement rocks is well below 1 km depth in that part of the area. The same easterly-tilted younger sedimentary bedrock layers described from the rest of Norfolk and Suffolk continue through this area but are even thicker, reaching over 500 m in parts of north-east Norfolk. They comprise interbedded sandstones and mudstones including the Gault Clay overlain by Chalk, which in places in the east is covered by further sands and clays. The lower sandstones and clays are thickest where they are exposed at the surface between Kings Lynn and Hunstanton reaching up to 75 m, however they thin out quickly when traced eastwards beneath the Chalk. The Chalk locally exceeds 450 m in thickness with the overlying sand and clay layers reaching 80 m thick but restricted to the fringes of the east Norfolk coast.

The further sedimentary bedrock layers described from the Fenland also continue eastwards beneath the Chalk and are not pinched out as they are to the south. Instead, they form a thickening sequence of layers to the east along the Norfolk coast.

Between Wells-next-the-Sea and Great Yarmouth, older sedimentary bedrock layers are also present at depth. These include sandstones, mudstones, and limestones of the Carboniferous Limestone and the Coal Measures. Elsewhere in Britain some of these layers are encountered nearer the surface and form important aquifers, however little is known about their water content beneath the North Norfolk coast and evidence from similar geological settings elsewhere in the UK suggest that it is likely to be saline.

Basement rocks[edit]

The basement rocks in this area are similar to those encountered below the other areas with grey mudstones and sandstones which have been changed by high temperatures and pressures in the long time since they were formed; thin layers of volcanic lavas have also been found in some boreholes. There may be a single granite intrusion in the area north of Fakenham based on the gravity and magnetic data, although other possible interpretations have also been suggested.