The BGS Lexicon of Named Rock Units — Result Details

Maidenhead Formation

Computer Code: MNHD Preferred Map Code: notEntered
Status Code: Full
Age range: Anglian Stage (QA) — Holocene Epoch (QH)
Lithological Description: Mainly river terrace sand and gravel, Brickearth silt and alluvial floodplain silt, silty clay and sand. The formation includes interbedded units (representing Interglacials) of locally fossiliferous silty sand, silt, together with organic clay, tufa and peat. River terrace deposits of the middle and lower Thames contain gravel clasts mainly composed of flint, vein quartz and local bedrock lithologies including chert. The terrace deposits are depicted on British Geological Survey maps using numbered terrace symbols. Modern British Geological Survey maps also show the terrace deposits as named units which are here interpreted as members of the Maidenhead Formation. The main terrace deposit members are the Black Park Gravel, Boyn Hill Gravel, Lynch Hill Gravel, Hackney Gravel, Taplow Gravel, Kempton Park Gravel, Shepperton Gravel and Staines Alluvium. Brickearth silt beds include the Enfield Silt, Roding Silt, Langley Silt, Dartford Silt, Crayford Silt and Ilford Silt.
Definition of Lower Boundary: Unconformable on glacigenic deposits of the Anglian stage or on older Pleistocene strata or bedrock. Individual terrace deposit members rest unconformably on older Pleistocene strata or bedrock.
Definition of Upper Boundary: Ground surface.
Thickness: Single terrace aggradations range from 3 to 12m. Interglacial beds (eg Trafalgar Square Beds) up to 12m.
Geographical Limits: The valley of the mainstream River Thames downstream of the Goring Gap, including the deposits of the valleys of the Blackwater, Lodden, Lea, Wandle, Mole, Godalming Wey, Bramley Wey, Darent and Cray. Deposits of the Kennet valley are referred to the Kennet Valley Formation.
Parent Unit: Thames Catchments Subgroup (THCAT)
Previous Name(s): Maidenhead Formation (MNHD)
Lower Thames Formation (-400)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Includes all of the mainstream terrace deposit members, Brickearth and floodplain alluvium of the middle and lower valleys of the River Thames and tributaries downstream of the Goring Gap to Gravesend. Gibbard, 45-58 in Bowen, 1999. 
Reference(s):
Gibbard, P L. 1999. The Thames Valley, its tributaries and their former courses. 45-58 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. [London: The Geological Society.] 
Ellison, R A, Woods, M A, Allen, D J, Forster, A, Pharaoh, T C and King, C. 2004. Geology of London. Memoir of the British Geological Survey, Sheets 256 (North London), 257 (Romford), 270 (South London), 271 (Dartford) (England and Wales). 
Bridgland, D R. 1994. Quaternary of the Thames. Geological Conservation Review Series No.7. (Peterborough: Joint Nature Conservation Committee.) 
McMillan, A A, Hamblin, R J O and Merritt, J W. 2005. An overview of the lithostratigraphical framework for the Quarternary and Neogene deposits of Great Britain (onshore). British Geological Survey Research Report RR/04/04. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E254 E255 E256 E257 E258 E268 E269 E270 E271 E284 E285 E286 E287 E301