The BGS Lexicon of Named Rock Units — Result Details

Thames Catchments Subgroup

Computer Code: THCAT 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 subgroup includes interbedded units of locally fossilferous silty sand, silt, together with organic clay, tufa and peat that are biostratigraphically correlated with interglacial (warm) stages. The subgroup is currently divided into the Upper Thames Valley Formation and the Maidenhead Formation (middle and lower Thames valley) for deposits of the main valley and some tributary valleys. The Kennet Valley Formation is established to terrace deposits of that valley. Terrace deposit gravel clasts are mainly limetone lithogies (upper Thames) and flint, vein quartz and local bedrock lithologies including chert (middle and lower Thames). 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 that are here interpreted as members of the relevant valley formation.
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.
Definition of Upper Boundary: Ground surface.
Thickness: Single terrace aggradations range from 3 to 12m. Interglacial units (eg: Trafalgar Square Member) up to 12m.
Geographical Limits: The valley of the mainstream River Thames and tributaries (Upper Thames Valley Formation, Maidenhead Formation). Separate formations are established for the deposits of some of the major tributaries of the Thames (eg: Kennet). The terrace deposits of the Medway Valley Formation (in the valley of the Medway) are also included within the subgroup. The Kesgrave Catchment Subgroup (Dunwich Group) includes all terrace deposits of the pre-Anglian, pre-diversionary ancestral River Thames.
Parent Unit: Britannia Catchments Group (BCAT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  All of the mainstream terrace deposit members. Brickearth and floodplain alluvium of the valley of the River Thames and tributaries. Gibbard, in Bowen, 1999. 45-58. 
Reference(s):
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.) 
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.] 
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:
E201 E218 E235 E236 E237 E238 E239 E252 E253 E254 E255 E256