The BGS Lexicon of Named Rock Units — Result Details

North Grimston Cementstone Member

Computer Code: NGRC Preferred Map Code: NGC
Status Code: Full
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Limestone, grey, thinly-bedded, muddy, interbedded in the west with thinly-bedded variably calcareous mudstone, in the east with flaggy calcareous sandstone. Generally poorly fossiliferous, although ammonites are known, and sponge spicules are common in the more calcareous beds.
Definition of Lower Boundary: In the Hambleton Hills, base a non-sequence, with interbedded muddy limestone and calcareous mudstone resting sharply on the eroded top of the rubbly coralliferous shelly limestone of the Coral Rag Member (Coralline Oolite Formation). In the type area in the Howardian Hills, interbedded muddy limestone and calcareous sandstone overlies grey and brown mudstone of the Langton Clay Member. In the Brown Moor Borehole (SE86SW/4 [81266 62043] ), calcareous siltstone rests sharply on the eroded top of fine-grained limestone inferred to represent the Malton Oolite Member (Coralline Oolite Formation).
Definition of Upper Boundary: In the Hambleton Hills, sharp change up from interbedded muddy limestone and calcareous mudstone into fine-grained sandstone, calcareous, spicule-rich, bioturbated, massive, ammonitiferous (Spaunton Sandstone Member). In the Howardian Hills and at Brown Moor Borehole, sharp change up into grey mudstone of Ampthill Clay Formation, probably a non-sequence.
Thickness: 9 to 13m in the Hambleton Hills, 16 to 22m in the Howardian Hills, 22.1m in the Brown Moor Borehole (SE86SW/4 [81266 62043]) (Gaunt et al., 1980), possibly including the underlying Langton Clay Member.
Geographical Limits: Southern part of the Cleveland Basin, North Yorkshire: southern end of the Hambleton Hills through Howardian Hills to North Grimston, overstepped southwards by Ampthill Clay Formation between Birdsall and Acklam, passes north and east into Newbridge and Spaunton Sandstone members.
Parent Unit: Upper Calcareous Grit Formation (UCG)
Previous Name(s): Cement-Stone (-3578)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Quarry south of Grimston Hill House, North Grimston, North Yorkshire. Exposed (1960s) 3m of interbedded calcareous sandstone and limestone. Wright, 1972, p. 258; Wright, 1976, p. 130. 
Reference Section  Snape Hill Quarry, Kilburn, North Yorkshire. Exposed (1990s) about 10.5m of thinly-bedded muddy limestone interbedded with thinly-bedded variably calcareous mudstone, base no longer seen, overlain by fine-grained, calcareous, spicule-rich sandstone (Spaunton Sandstone Member of Upper Calcareous Grit Formation). Wilson (1933) reports 42 feet (12.8m) of beds resting on the Coral Rag [Member]. Wright and Cox, 2001, pp 170-173; Wilson, 1933, p. 503, beds 2 to 4. 
Reference(s):
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.) 
Gaunt, G D, Ivimey-Cook, H C, Penn, I E and Cox, B M. 1980. Mesozoic rocks proved by the Institute of Geological Sciences boreholes in the Humber and Acklam areas. Report of the Institute of Geological Sciences, No. 79/13. 
Wilson, V. 1933. The Corallian rocks of the Howardian Hills. Quarterly Journal of the Geological Society of London, Vol. 89, 480-507. 
Wright, J K. 1972. The stratigraphy of the Yorkshire Corallian. Proceedings of the Yorkshire Geological Society, Vol. 39, 225-266. 
Wright, C D. 1976. New outcrops of Ampthill Clay north of Market Weighton, North Yorkshire, and their structural implications. Proceedings of the Yorkshire Geological Society, Vol. 41, 127-140. 
Wright, J K. 2009. The geology of the Corallian ridge (Upper Jurassic) between Gilling East and North Grimston, Howardian Hills, North Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 57, 193-216. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E063 E064