London Basin

Coordinates: 51°45′50″N 0°26′42″E / 51.764°N 0.445°E / 51.764; 0.445
Source: Wikipedia, the free encyclopedia.

Geological map of the London Basin

The London Basin is an elongated, roughly triangular

period
and was mainly active between 40 and 60 million years ago.

Boundaries and shape

Spatial boundaries

The generally accepted boundaries are the

North Sea Basin, extending on land along the north Kent coast to Reculver and up the east coast of Essex and into Suffolk, where it is overlain by Pleistocene 'Crag' deposits which cover much of eastern Suffolk and Norfolk and are better considered as part of the North Sea Basin.[1]
[2]

The axis of the basin runs west–east from Marlborough and Newbury (Berkshire) to Chertsey (Surrey) before swinging slightly north of east through Westminster, passing midway between Chelmsford and Southend-on-Sea (Essex) to the east coast between the estuaries of the Crouch and the Blackwater.[3] Though north of the current mouth of the Thames, this line is well to the south of the centre-line of the basin which is asymmetric, its southern limb dipping more steeply than the northern.[4]

Geological boundaries

Geologic map of southeast England and the region around the English Channel, showing the London Basin in its regional context.

The Basin formed on top of the Late Cretaceous

artesian basin
, with fresh water springs emerging on the bed of the
Bagshot Beds
etc., forming sandy heaths.

Tectonic history

London Platform

See also:
London-Brabant Massif
Lower Cretaceous
sequence. Vertical exaggeration 1:5.

Most of the basin is underlain at depth by a block of

Gault Formation
. The whole area remained submerged during much of the Late Cretaceous, though the Chalk contains levels indicating periods of erosion.

During the

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.[3]

Sedimentary infill and stratigraphy

The London Basin is mainly filled with Palaeogene

ages. The Lambeth Group consists of the Upnor Formation, the Woolwich Formation and the Reading Formation
.

The Lambeth Group is overlain by the

environments
and were deposited during the Ypresian age (55.8 – 48.6 million years ago).

On top of the Thames Group is the

facies rocks. It can be up to 140 metres thick[7] and is of late Ypresian to Lutetian
age.

Geography

Drainage

The basin is mainly drained by the

Vale of Aylesbury. The main headstream within the London Basin proper is the Kennet, which flows along the axis from the Marlborough area, joining the Thames at Reading
.

To the south rivers such as the

Mole and Medway, draining from the Weald, cut through the North Downs into the basin; these are presumed to date from before the erosion of the Weald dome.[8]

During the

Anglian Stage. The north eastern part of the basin is now drained to the North Sea by rivers including the Crouch, Blackwater, Stour and Orwell
.

Settlements

Much of the basin is urbanised. Besides the whole

Bishops Stortford, Harlow, Hertford, Stevenage, Harpenden, Hatfield, Welwyn Garden City, Potters Bar, St Albans, Luton and High Wycombe
.

References

  1. ISBN 0-85272-478-0
  2. ISBN 978-0-7518-1899-4
    (flat)
  3. ^
    ISBN 0-11-884522-5
  4. ^ Thames Estuary: Sheet 51N 00 Solid Geology, 1:250,000 Geological map series, British Geological Survey, Keyworth, 1989
  5. ^ For the dating of the Thanetian age: see Gradstein et al. (2004)
  6. ^ Brenchley & Rawson (2006), p 396
  7. ^ Jackson (2008), p 71
  8. ISBN 0-12-388950-2
  9. ^ "2011 Census - Built-up areas". ONS. Retrieved 28 January 2014.

Literature

51°45′50″N 0°26′42″E / 51.764°N 0.445°E / 51.764; 0.445

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