The BGS Lexicon of Named Rock Units — Result Details

Stewartby Member

Computer Code: SBY Preferred Map Code: Sby
Status Code: Full
Age range: Callovian Age (JC) — Callovian Age (JC)
Lithological Description: Predominantly pale to medium grey, commonly smooth, variably silty, calcareous, poorly fossiliferous, blocky mudstones. Subordinate beds of silty mudstones packed with immature shells of the bivalve Bositra buchii (Roemer). Thin, calcareous siltstones, particularly in upper part, commonly with Gryphaea. Ammonites and other macrofauna generally pyritised.
Definition of Lower Boundary: At top of highest brownish-grey, organic rich mudstone within thinly interbedded transition (to c.3m thick) to brownish-grey, fissile mudstones of underlying 'Lower Oxford Clay'(Peterborough Member). More or less arbitrary in field mapping.
Definition of Upper Boundary: At the top of the Lamberti Limestone (where present) or an equivalent shell bed or siltstone. The horizon is clear on geophysical logs. Change in Gryphaea faunas (G.lituola, below to G. dilatata, above) and ammonite faunas. (Kosmoceras, below: Cardioceras, above) useful supportive indicators. Base of Weymouth Member.
Thickness: 0 - c.50m.
Geographical Limits: Dorset to Humberside.
Parent Unit: Oxford Clay Formation (OXC)
Previous Name(s): Middle Oxford Clay (-4317)
Middle Oxford Clay Member [Obsolete Name And Code: See SBY] (MOXC)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Former brickpit at Woodham, Bucks. (Well-known in literature, eg Arkell 1939, Callomon, 1968, Hudson and Palframan, 1969, and collections). 
Reference Section  Marston Vale BH 3A (Rectory Farm) (BGS registration no. SP94SE/110), Beds. Depth c.4.30-31.36m. 
Type Section  London Brick Co. Rookery Pit, Stewartby, Beds. 
Reference(s):
Cox, B M, Hudson, J D and Martill, D M, 1992. Lithostratigraphic nomenclature of the Oxford Clay (Jurassic). Proceedings of the Geologists' Association, Vol.103, p.343-345. 
Martell, D M and Hudson, J D, (Editors), 1991. Fossils of the Oxford Clay. Palaeontological Association Field Guide to Fossils No.4. 
Callomon, J H, 1968. The Kellaways Beds and the Oxford clay. In Sylvester-Bradley, P C and Ford, T D. (Editors). The Geology of the East Midlands. (Leicester: Leicester University Press). 
Arkell, W J, 1939. The ammonite succession at the Woodham Brick Company's Pit, Akeman Street Station, Buckinghamshire, and its bearing on the classification of the Oxford Clay. Quarterly Journal of the Geological Society of London, Vol.95, 135-222. 
Hudson, J D and Palframan, D F B, 1969. The ecology and preservation of the Oxford Clay fauna at Woodham, Buckinghamshire. Quarterly Journal of the Geological Society of London, Vol.124, p.387-418. 
Wyatt, R J, Moorlock, B S P, Lake, R D and Shephard-Thorn, E R, 1988. Geology of the Leighton Buzzard - Ampthill district. British Geological Survey Technical Report, WA/88/1. 
Berridge, N G, Pattison, J, Samuel, M D A, Brandon, A, Howard, A S, Pharaoh, T C and Riley, N J. 1999. Geology of the Grantham district. Memoir of the British Geological Survey, sheet 127 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E127 E237 E159 E219