The geology of Norfolk, a county in eastern England, is characterised by a sequence of late Mesozoic and Cenozoic sedimentary rocks of marine origin, largely concealed beneath extensive Quaternary superficial deposits.
Bedrock geology
The oldest exposed rocks are late Jurassic mudstones and muddy limestones situated west of King’s Lynn and Downham Market. Overlying these are Cretaceous strata, beginning with the Wealden Group of mudstones, limestones, siltstones and sandstones, which extends from Hunstanton southward to the vicinity of Southery. A narrow east‑west band of Lower Greensand sandstones occurs immediately east of the Wealden outcrop, followed stratigraphically by the Gault and Upper Greensand formations. The Chalk Group, comprising the Grey and White Chalk subgroups, overlies the Greensand and extends across most of Norfolk east of a line from Holme‑next‑the‑Sea to Hockwold cum Wilton, although it is obscured by later Neogene sediments in the eastern part of the county. Small exposures of Palaeogene Eocene clay of the Thames Group are recorded near Loddon.
In the eastern county a sequence of shelly sand, clay and gravel deposits, collectively known as “crag”, is present. The crag succession is divided into the Red Crag, Norwich Crag and Wroxham Crag formations, which are of Pliocene to Pleistocene age and represent some of the youngest sedimentary rocks in Britain.
A granite pluton associated with the Acadian orogeny is inferred beneath central and western Norfolk, although it is not exposed at the surface.
Superficial and Quaternary deposits
The majority of Norfolk’s surface is covered by unconsolidated Quaternary sediments. The oldest of these are glacial tills deposited during the Anglian glaciation, interbedded with sheets of glacial sands and gravels. The Anglian ice sheet’s erosive action is thought to have reduced the height of the East Anglian Chalk scarp relative to its outcrops in Lincolnshire and the Chiltern Hills.
Later, the Devensian glaciation produced an ice sheet that reached the north coast of Norfolk, leaving further glacial deposits. Subsequent alluvial sediments fill the main river valleys and the extensive flats of the Norfolk Broads, while coastal alluvium lines the north coast from Holme‑next‑the‑Sea to Brancaster. Fluvial terrace deposits are evident in valleys such as that of the River Waveney.
Aeolian processes have generated blown sand on the lower coastal sections, and widespread peat occurs in the fenland areas south and west of Downham Market.
Geological significance
Norfolk’s geology records a transition from Jurassic marine mudstones through Cretaceous terrestrial and marginal marine deposits to extensive Cenozoic chalk and Pliocene–Pleistocene marine “crag” formations, all subsequently modified by repeated glaciations and post‑glacial sedimentary processes. The concealed nature of much of the bedrock beneath thick Quaternary deposits makes the county a notable example of the interplay between deep geological history and recent surface processes in eastern England.
