London Basin - Tectonic History

Tectonic History

Most of the basin is underlain at depth by a block of Palaeozoic rocks known as the London Platform. This is separated by faulting from the Early Cretaceous Wessex Basin (underlying the Weald and Hampshire Basin) to the south and the Worcester Basin to the west. Vertical movements of this block have affected both deposition and structure, with the result that many of the Mesozoic rocks underlying the neighbouring Weald are not present, or are very much thinner. Rocks of Triassic age are absent under London, occurring at depth only at the western edge of the basin. Jurassic rocks occur over a wider area to the west and south but are also absent under London itself. During Early Cretaceous times the platform was uplifted and eroded, with the erosional material deposited to the south as the Wealden Group. Sea level rose during deposition of the Lower Greensand Group, but only completely covered the platform during deposition of the Gault Formation. The whole area remained submerged during much of the Late Cretaceous, though the Chalk contains levels indicating periods of erosion.

During the Palaeogene the south-east of England was affected by movements related to the formation of the Alps (the Alpine Orogeny). One consequence of this was relative vertical movements, with the eastern part of the Wessex Basin being uplifted as the Weald-Artois Anticline and the London Platform subsiding to form the London Basin. Up to 320 metres (1,050 ft) of Palaeocene and Eocene sediments were deposited in the basin. The Pleistocene saw the sea retreat from the basin as global sea-level fell due to accumulation of ice sheets.