The Pleistocene evolution of the Thames and Rhine drainage systems in the southern North Sea Basin

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Abstract During most of the Middle and Late Pleistocene, global climate was colder than at present. At such times, sea-level was very much lower and the southern North Sea was land, drained by the same rivers that today issue into the sea from Britain and north-west Europe. Evidence from onshore in Britain suggests that the Thames did not drain into the southernmost part of the North Sea Basin until the early Middle Pleistocene; prior to that it flowed across East Anglia and northwards across the area of the present north Norfolk coast. It is thought that the lowland between Kent, East Anglia and the Continent was at this time drained by the ‘Lobourg River’, which arose on the northern flanks of the Wealden ridge and drained northwards into what is now the southern North Sea. The early Medway is thought to have joined this Lobourg River in the area that now lies offshore from southeast Suffolk. It seems that by the early Middle Pleistocene the Thames had adopted this course of the Medway and with it, therefore, the confluence with the Lobourg. It is widely believed that Anglian/Elsterian ice-sheets caused proglacial ponding in the southern North Sea basin and that a large lake formed, fed by the Thames-Medway and Rhine river systems. It has also been suggested that this lake overflowed to the southwest into the English Channel Basin, breaching the Chalk ridge and initiating a through route via the Strait of Dover, a route that was used by the Rhine-Thames drainage system during all subsequent low-sea-level episodes. Middle and Upper Pleistocene deposits of both the Thames and Rhine systems are preserved in the areas immediately offshore from Britain, The Netherlands and Belgium and can be traced from both sides towards the axial channel of the North Sea Basin, the formation of which was perhaps initiated by the Lobourg River. Although the Rhine’s offshore deposits, in particular, appear to follow a route that heads southwards, towards the Strait of Dover, no sedimentary evidence has yet been found that demonstrates a late Pleistocene fluvial course either through this strait or, conversely, into the North Sea.