Quaternary vertical crustal motion and drainage evolution in East Anglia and adjoining parts of southern England: chronology of the Ingham River terrace deposits

Abstract

Prior to its disruption during the Anglian glaciation (MIS 12), the Ingham or Bytham River used to flow eastwards across central England and East Anglia into the southern North Sea. It thus had a much larger catchment than any extant river system in Britain; its headwaters may well have been as far away as North Wales and/or NW England. Terrace deposits of this former river system crop out across East Anglia and, as for any other river, can be used to investigate uplift, landscape evolution and the physical properties of the underlying continental crust. However, such an investigation has hitherto been hampered by inconsistencies between different authors' terrace schemes; furthermore, and controversially, one such scheme has formed the basis for the inference that the region was affected by a pre‐Anglian (MIS 16) glaciation. By re‐examining the raw data, the Ingham River deposits are shown to be disposed in three terraces, inferred to date from MIS 16, 14 and 12. The evidence previously attributed to pre‐Anglian glaciation is associated with the youngest of these terraces, and thus marks the MIS 12 (i.e. Anglian) glaciation; the argument for glaciation of the region in MIS 16 is thus an artefact of previous miscorrelation of the terrace deposits. It is inferred that development of the very large Ingham River was synchronous with decapitation of the former ‘Greater Thames’, or ‘High‐level Kesgrave Thames’ river, some time between MIS 18 and MIS 16. Uplift histories at representative localities across East Anglia have been modelled using composite data sets, combining the terrace deposits of the Ingham River and of the post‐Anglian rivers Lark and Waveney. The sites modelled are typefied by much faster uplift in the early Middle Pleistocene than in the late Middle Pleistocene; this effect is shown to be a consequence of the relative thinness (no more than ∼7–8 km thick) of the mobile lower‐crustal layer, itself a consequence of the low surface heat flow in the London Platform crustal province. The post‐Early Pleistocene uplift tapers eastward, consistent with the observed downstream convergence of the Ingham and Waveney terraces, and is close to zero near the modern coastline around Lowestoft and Great Yarmouth. Stratigraphic relationships between the Ingham terrace deposits and temperate‐stage marine and terrestrial deposits in this coastal area allow sites to be dated; thus, Pakefield and Corton date from MIS 15, whereas Norton Subcourse dates from MIS 17. The oldest known Lower Palaeolithic sites in the region, characterized by flake artefacts, are Pakefield (MIS 15) and Hengrave (?MIS 14); younger pre‐Anglian sites that have yielded handaxes and/or fossil material of the water vole Arvicola cantiana date from MIS 13. The minimal vertical crustal motion in this coastal area, where temperate‐stage deposits from different climate cycles crop out close to present‐day sea level, does not imply high crustal stability; instead, it indicates a ‘hinge zone’ between the uplifting hinterland and the subsiding depocentre in the southern North Sea.