The BGS Lexicon of Named Rock Units — Result Details

Sudbury Formation

Computer Code: SBRY Preferred Map Code: notEntered
Status Code: Full
Age range: Early Pleistocene Epoch (QPE) — Mid Pleistocene Epoch (QPM)
Lithological Description: Formation encompasses fluvial, lacustrine and organic deposits of the pre-diversionary River Thames. 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 formation represents the first significant input of far-travelled materials into the Thames river sediments, and is characterised by quartz and quartzite from the Triassic, Carboniferous and Devonian rocks of the West Midlands, Welsh Borderland and possibly southwestern Pennines, and felsic volcanic rocks from northern Wales. The presence of mega-erratics and glacially fractures sand grains indicate glacial erosion in the headwater regions of the river. The fluvial gravels occupy terrace levels and the 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 10m.
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.
Thickness: c.18m. Individual terrace aggradations typically 5-10m thick.
Geographical Limits: Formation is restricted to the Thames Valley, Essex and Suffolk. It does not extend into Norfolk (Hamblin and Moorlock, 1995).
Parent Unit: Kesgrave Catchment Subgroup (KGCA)
Previous Name(s): Essex White Ballast (-3284)
Kesgrave Formation [Obsolete Code: Use KES] (-1621)
Kesgrave Sands And Gravels [Obsolete Name And Code: See KGCA] (KGSG)
Alternative Name(s): Waterman's Lodge Member
Beaconsfield Member
Stoke Row Member
Gerrards Cross Member
Westland Green Member
Satwell Member
Stratotypes:
Type Area  The course of the pre-diversionary River Thames from Stebbing, Essex to Claydon, Suffolk. Whiteman and Rose, 1992. 
Reference(s):
Whiteman, C A and Rose, J. 1992. Thames river sediments of the British Early and Middle Pleistocene. Quarterly Science Reviews, Vol.11, 363-375. 
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. 1994. Major river systems of central and southern Britain during the Early and Middle Pleistocene. Terra Nova, Vol.6, 435-443. 
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. 
Pattison, J, Berridge, N G, Allsop, J M and Wilkinson, I P. 1993. Geology of the country around Sudbury (Suffolk). Memoir of the British Geological Survey, Sheet 206 (England and Wales). 
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.] 
Kemp, R A. 1987. Genesis and environmental significance of a buried Middle Pleistocene soil in eastern England. Geoderma, Vol.41, 49-77. 
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. 1985. The Valley Farm Soil in southern East Anglia. 179-196 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:
E206 E207 E208 E221 E222 E223 E239 E240 E255 E256 E257