The BGS Lexicon of Named Rock Units — Result Details

Middle Calcareous Grit Member

Computer Code: MCG Preferred Map Code: MCG
Status Code: Full
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Sandstone, fine-grained, bedded, clayey in lower part passing calcareous and shelly upwards with scattered ooids, generally poorly fossiliferous; locally a sandy ooidal limestone with trigoniid bivalves, gastropods and ammonites is developed at the top (Newbridge Trigonia Bed; Coe, 1995, p. 169).
Definition of Lower Boundary: Conformable: sharp change upwards into calcareous fine-grained sandstone from sandy ooidal limestone (Hambleton Oolite Member). Where this is absent, difficult to distinguish from Birdsall Calcareous Grit Member.
Definition of Upper Boundary: Conformable or non-sequence: sharp change up from calcareous fine-grained sandstone or locally a sandy ooidal limestone (Newbridge Trigonia Bed) into generally non-sandy ooidal limestone (Malton Oolite Member), at the base of a black ooid-limestone bed at Newbridge Quarry (Coe, 1995).
Thickness: 12 to 15m in the Tabular Hills thinning to zero south of Malton and near Scarborough, less than 2m at Spiker's Hill Quarry.
Geographical Limits: Central and western Cleveland Basin, North Yorkshire, overstepped eastwards by Malton Oolite Member.
Parent Unit: Coralline Oolite Formation (COO)
Previous Name(s): Middle Calcareous Grit (-4183)
Alternative Name(s): none recorded or not applicable
Reference Section  Spikers Hill Quarry, West Ayton, North Yorkshire. Exposes entire member, 1.17m thick, comprising bedded clayey fine-grained sandstone, underlain by Hambleton Oolite Member, non-sequentially overlain by Malton Oolite Member. Type Section proposed here; Wright, 1972, p.237; Wright and Cox, 2001, pp 157-161. 
Reference Section  Newbridge Quarry, Pickering, North Yorkshire. Exposes upper part of member, about 2.3m thick, comprising siltstone, overlain by sandy, shelly ooidal limestone and ooidal fine-grained sandstone (Newbridge Trigonia Bed), overlain by Malton Oolite Member. Nearby [SE 8017 8565], the lower part, bioturbated fine-grained sandstone beds are exposed. Coe, 1995 
Type Section  Love Lane Quarry, Pickering, North Yorkshire. 5m of massive, calcareous sandstone is currently seen with the Newbridge Trigonia Bed clearly visible near the top, with a conformable upward transition into the Malton Oolite Member. Formerly exposed up to 8.5m of strata but base not seen. Blake and Hudleston, 1877, pp 334-336; Arkell, 1933, pp 426-427. 
Coe, A L. 1995. A comparison of the Oxfordian successions of Dorset, Oxfordshire and Yorkshire. 151-172 in Taylor, P D (Ed.) Field Geology of the British Jurassic. [Bath: The Geological Society.] 
Wright, J K, and Cox, B M. 2001. British Upper Jurassic Stratigraphy (Oxfordian to Kimmeridgian). Geological Conservation Review Series. No. 21. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
Blake, J F and Huddleston, W H 1877. On the Corallian rocks of England. Quarterly Journal of the Geological Society of London, Vol.33, 260-405. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
Rawson, P F and Wright, J K. 1995. Jurassic of the Cleveland Basin, North Yorkshire. 173-208 in Taylor, P D (Ed.) Field Geology of the British Jurassic. (London: Geological Society.) 
Wright, J K. 1972. The stratigraphy of the Yorkshire Corallian. Proceedings of the Yorkshire Geological Society, Vol. 39, 225-266. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E043 E044 E052 E053 E054