| Computer Code: |
THCAT |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Anglian Stage (QA)
— Holocene Epoch (QH) |
| Lithological Description: |
The Thames Catchments Subgroup comprises river terrace deposits of Anglian and younger age of the River Thames and its tributaries. Mass movement deposits and organic deposits (organic clay, tufa and peat) of the catchments are also included. The Thames river system is one of the most intensively studied in Britain. Organic fossiliferous beds interbedded with the 'cold stage' terrace sand and gravel aggradations have been correlated with interglacial 'warm stages' allowing the establishment of a detailed climate-related stratigraphical framework.
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. Terrace deposit gravel clasts are mainly limestone lithogies (upper Thames) and flint, vein quartz and local bedrock lithologies including chert (middle and lower Thames).
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 and the Medway Valley Formation is established for terrace deposits of those valleys. 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.
Anglian to Holocene (MIS 12-1). |
| 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 12 m. Interglacial units are up to 12 m thick. |
| 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): |
| 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. |
| McMillan, A A. 2005. A provisional Quaternary and Neogene lithostratigraphical framework for Great Britain. (Netherlands: Journal of Geosciences), 84-2, 87-107. |
| McMillan, A A, Hamblin, R J O, and Merritt, J W. 2011. A lithostratigraphical framework for onshore Quaternary and Neogene (Tertiary) superficial deposits of Great Britain and the Isle of Man. British Geological Survey Research Report, RR/10/03. 343pp. |
| Stoker, M S, McMillan, A A and Waters, C N. Quaternary Stratigraphical Chart: Southern Britain. British Geological Survey, 1 poster. |
| 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
|
