This article reviews the sedimentation and stratigraphical relationships of the Anglian Stage North Seab Drift Formation Corton Sands, Leet Hill Gravel and associated deposits, and their relationship to the glacial events in the region. The meltwater sand and gravel units underlie a substantial area of E Norfolk and NE Suffolk and are associated with the North Sea Drift Formation diamictons. Critical sequences showing the stratigraphical relationships are presented and their relationship to the Ingham (‘Bytham’) Formation Kirby Cane Member gravel is discussed, the latter being deposited by the Ingham (‘Bytham’) river. The Kirby Cane unit is shown to be the youngest ‘Bytham river terrace’ element. The advance of the North Sea Drift ice towards the SW brought Scandinavian erratics. It blocked this river and extended inland depositing the Norwich Brickearth, Starston Till and equivalents. That the Corton Member sands, and the Leet Hill Gravels, were derived from the North Sea Drift Formation ice is indicated by heavy-mineral assemblages, pebble assemblages, fossil assemblages and the presence of diamicton clasts of North Sea Drift-type material. The diamicton sediment was derived from the floor of North Sea and SW Scandinavian peninsula. Following the ice retreat, the river re-occupied its course. During glaciation the water-level rose in the North Sea basin, where a lake was dammed by the ice, so that as the Happisburgh Diamicton ice melted, the water submerged the diamicton surface and flooded the district. Continued flooding of the ‘Corton embayment’ in eastern Norfolk and north Suffolk resulted in the drowning of the landscape allowing the Corton Member sands to be deposited, forming a massive braided sand-delta complex. The meltwater sands were derived from continued North Sea Drift Formation glaciation in N Norfolk, and they were deposited by meltwater streams that flowed towards the E and later towards the SE. Here the streams entered the vast southern North Sea freshwater lake. The presence of periglacial structures in the sands indicates that sedimentation kept pace with creation of new accommodation space as the water-level in the basin rose. The depth of water in the lake reached at least +32 m a.s.l. at its maximum and possibly higher. The possible impact of isostatic depression of the basin is discussed. Subsequent advance of the Lowestoft Formation ice overrode the Corton and associated sequences, and also locally entered the lake. Once established the North Sea lake persisted throughout the period of later glaciation as demonstrated by deposition of the Oulton Beds and Aldeby Member deposits in the Corton district. Through this the palaeogeographical and palaeoenvironmental evolution and more particularly, the relationship of the Anglian-age glaciers and their meltwater to the North Sea basin lake are discussed. |
