The BGS Lexicon of Named Rock Units — Result Details

Ancholme Group

Computer Code: AMG Preferred Map Code: AmG
Status Code: Full
Age range: Callovian Age (JC) — Kimmeridgian Age (JD)
Lithological Description: Predominantly grey, marine mudstone and silty mudstone; beds of argillaceous limestone nodules (or more or less persistent beds) at some levels; units of siltstone and sandstone at some levels, widespread near base (in Kellaways Formation), in middle part (West Walton Formation) and more locally at other levels (notably Kimmeridge Clay Formation of Oxon/Buckinghamshire); shelly marl, limestone and sandy limestone developed locally (notably in the West Walton Formation).
Definition of Lower Boundary: Base of Kellaways Formation; commonly a shelly mudstone resting on limestone of the Cornbrash Formation.
Definition of Upper Boundary: Unconformable junction of mudstones with uppermost Jurassic/Lower Cretaceous limestones and sandstones; in the southwest (Oxon/Buckinghamshire) Kimmeridge Clay Formation overlain by Portland Formation; farther north, Ancholme Group progressively overstepped towards the Market Weighton High.
Thickness: Probably zero (over Market Weighton High) to c.350m in central/eastern Lincolnshire (Louth district, Sheet 103), about 150-180m in Oxon/Buckinghamshire.
Geographical Limits: Waddesdon, Buckinghamshire, between Oxford and Aylesbury (Thame district, Sheet 237), where Corallian Group wedges out (Horton, A, et al, 1995) to Market Weighton area, Yorkshire (Sheet 72). N.B. Mutually exclusive with the Corallian Formation/Group, thus not used south of Oxford, nor in the Cleveland Basin.
Parent Unit: Not Applicable (-)
Previous Name(s): Ancholme Clay Group [Obsolete Name and Code: Use AMG] (-3165)
Alternative Name(s): none recorded or not applicable
Type Area  Vale of Ancholme, north Lincolnshire (Brigg district; Sheet 89) (Gaunt et al., 1992). 
Reference Section  Nettleton Bottom Borehole (TF19NW/54) (Cox, 1992; Gaunt et al., 1992). See also entries for component formations (Kellaways, Oxford Clay, West Walton, Ampthill Clay, Kimmeridge Clay). 
Gallois, R W and Cox, B M, 1976. The stratigraphy of the Lower Kimmeridge Clay of eastern England. Proceedings of the Yorkshire Geological Society, Vol.41, 13-26. 
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
Cox, B M. 1992. Appendix 4: Ancholme Clay Group Biostratigraphy. 145-148 in Geology of the country around Kingston upon Hull and Brigg. Gaunt, G D, Fletcher, T P, and Wood, C J. Memoir of the British Geological Survey, Sheets 80 and 89 (England and Wales). 
Gallois, R W and Cox, B M, 1974. Stratigraphy of the Upper Kimmeridge Clay of the Wash area. Bulletin of the Geological Survey of Great Britain. No.47, 1-28. 
Horton, A, Sumbler, M G, Cox, B M and Ambrose, K, 1995. Geology of the country around Thame. Memoir of the British Geological Survey, Sheet 237 (England and Wales). 
Gallois, R W. 1979. Geological investigations for the Wash Water Storage Scheme. Report of the Institute of Geological Sciences, 78/19, 1-74pp. 
Gaunt, G D, Fletcher, T P and Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 172pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E081 E090 E091 E072 E080 E089 E115 E128 E103 E127 E144 E172 E237 E281 E341 E342