The BGS Lexicon of Named Rock Units — Result Details

Kesgrave Catchment Subgroup

Computer Code: KGCA Preferred Map Code: notEntered
Status Code: Full
Age range: Early Pleistocene Epoch (QPE) — Mid Pleistocene Epoch (QPM)
Lithological Description: Encompasses fluvial, lacustrine and organic deposits of the pre-diversionary River Thames, and the pre-glacial soils developed on such deposits. Most of the surviving deposits are fluvial gravels, with sedimentary structures indicating deposition by a braided river. Lacustrine silts and clays and organic peats are uncommon. The gravels are characterised by quartz and quartzite from the Triassic, Carboniferous and Devonian rocks of the West Midlands, Welsh Borderland and possibly southwestern Pennines, and by felsic volcanic rocks from northern Wales. The presence of mega-erratics and glacially-fractured sand grains indicate glacial erosion in the headwater regions of the river. The fluvial gravels occupy terrace levels and formations and members are defined on the basis of altitude and pebble clast content. The members comprise bodies of cross-bedded and massive, moderately sorted sand and gravel. The aggradations are generally entrenched into bedrock with a difference in surface elevation of at least 5m. The upper part of the gravels which dominate the subgroup are commonly affected by pedogenesis. The Valley Farm Soil is a rubified and clay-enriched horizon affecting the top 1.0-1.5m and indicating warm interglacial conditions. The Barham Arctic Structure Soil is a complex pedogenic horizon affecting the topmost 1.0-1.5m of the subgroup and of the Valley Farm Soil (Rose and Allen 1976, Rose et al 1985).
Definition of Lower Boundary: Unconformable on bedrock: Cretaceous, Palaeogene and Crag Group. Differentiation from the Crag Group can be difficult where the latter is reworked, and the distinction must be made on the basis of sedimentological structures: the Crag Group is marine, the Kesgrave Catchment Subgroup is fluvial.
Definition of Upper Boundary: Commonly overlain by Mid Pleistocene glacigenic deposits. Upper boundary may be difficult to determine where overlain by glaciofluvial sand and gravel, but the presence of more angular clasts, chalk, and poorer sorting in the latter is usually helpful. The uppermost 1.0-1.5m of the subgroup is commonly marked by the Valley Farm Soil and/or the Barham Arctic Structure Soil.
Thickness: c.21.3m aggregate thickness with individual terrace aggradations typically 5-12m thick.
Geographical Limits: The unit is restricted to the Thames Valley, Essex and Suffolk. BGS 1:50 000 Sheets 206-208, 221-225, 239-242, 255-257. It does not extend into Norfolk.
Parent Unit: Dunwich Group (DUNW)
Previous Name(s): Kesgrave Formation [Obsolete Code: Use KES] (-1621)
Kesgrave Formation (B) [Obsolete Name And Code: See KGCA] (KES)
Kesgrave Formation (A) [Obsolete Name And Code: See KGCA] (KESF)
Kesgrave Sands And Gravels [Obsolete Name And Code: See KGCA] (KGSG)
Essex White Ballast (-3284)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Gravel pit at Kesgrave. Rose and Allen, 1977. 
Reference(s):
Hamblin, R J O, and Moorlock, B S P. 1995. The Kesgrave and Bytham Sands and Gravels of eastern Suffolk. Quaternary Newsletter, No.77, 17-31. 
Kemp, R A. 1987. Genesis and environmental significance of a buried Middle Pleistocene soil in eastern England. Geoderma, Vol.41, 49-77. 
Kemp, R A. 1985. The Valley Farm Soil in southern East Anglia. 179-196 in Boardman, J (editor), Soils and Quaternary landscape evolution. [Chichester: Wiley.] 
Whiteman, C A and Rose, J. 1992. Thames river sediments of the British Early and Middle Pleistocene. Quarterly Science Reviews, Vol.11, 363-375. 
Rose, J. 1994. Major river systems of central and southern Britain during the Early and Middle Pleistocene. Terra Nova, Vol.6, 435-443. 
Rose, J, Allen, P and Hey, R W, 1976. Middle Pleistocene stratigraphy in Southern East Anglia. Nature, Vol.236, p.492-494. 
Rose, J and Allen, P, 1977. Middle Pleistocene stratigraphy in south-east Suffolk. Quarterly Journal of the Geological Society of London, Vol.133, p.83-102. 
Whiteman, C A. 1992. The palaeogeography and correlation of pre-Anglian-Glaciation terraces of the River Thames in Essex and the London Basin. Proceedings of the Geologists' Association, Vol.103, 37-56. 
Rose, J, Whiteman, C A, Allan, P and Kemp, R A. 1999. The Kesgrave Sands and Gravels: 'pre-glacial' Quaternary deposits of the River Thames in East Anglia and the Thames Valley. Proceedings of the Geologists' Association, Vol.110, 93-116. 
Rose, J, Allen, P, Kemp, R A, Whiteman, C A and Owen, N. 1985. The early Anglian Barham Soil in southern East Anglia. 197-229 in Boardman, J (editor), Soils and Quaternary landscape evolution. [Chichester: Wiley.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable