The BGS Lexicon of Named Rock Units — Result Details

Malton Oolite Member

Computer Code: MTOL Preferred Map Code: MO
Status Code: Full
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Ooidal limestone, white to grey, variably bioclastic; high-energy facies generally an ooid-grainstone or packstone, fine- to coarse-grained, thick- and cross-bedded, poorly fossiliferous, lower energy facies variably shelly, variably finely sandy, thin- to medium-bedded, with thin fine-grained calcareous sandstone and silty mudstone beds. Fauna notably of ammonites, bivalves, gastropods and locally corals.
Definition of Lower Boundary: Conformable or non-sequence: sharp change up from calcareous fine-grained sandstone (Middle Calcareous Grit Member) or locally a sandy ooidal limestone (Newbridge Trigonia Bed of Middle Calcareous Grit Member) into generally non-sandy ooidal limestone (Malton Oolite Member), at the base of a black ooid-limestone bed at Newbridge Quarry (Coe, 1995). Where Middle Calcareous Grit Member absent, it may be locally distinguished from the ooidal limestone of the Hambleton Oolite Member (Coralline Oolite Formation) by its coarser grain size and better sorting (Wright, 2009). Locally west of Malton in the Howardian Hills, the Malton Oolite Member rests non-sequentially on fine-grained porcellanous limestone of the Hildenley Limestone Member (Coralline Oolite Formation) (Wright, 2009, p. 199).
Definition of Upper Boundary: Non sequence or erosional disconformity: generally a poorly to moderately shelly ooid-limestone sharply overlain by a moderately to highly fossiliferous, moderately ooidal, lime-muddy, bioclastic limestone (Coral Rag Member, Coralline Oolite Formation); locally boulders of Malton Oolite may be set in Coral Rag limestone (Wright, 1972, p. 241). Where the Coral Rag is absent in the south of the Howardian Hills, Malton Oolite Member sharply overlain by mudstone (Langton Clay Member) or sandstone (Limekiln Member), all of Upper Calcareous Grit Formation.
Thickness: 0 to 40m: Filey area more than 25m, Tabular Hills 6 to 14m thickening east, Hambleton Hills 6 to 17m, Howardian Hills 0 to 40m.
Geographical Limits: Cleveland Basin, North Yorkshire: as far south as Langton area, possibly overstepped southwards by the Upper Calcareous Grit.
Parent Unit: Coralline Oolite Formation (COO)
Previous Name(s): Osmington Oolite (-3567)
Chemnitzia Oolite/Limestones (-4207)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Leysthorpe Quarry, Nunnington, North Yorkshire: exposes 16.6m of the member, overlain by the Coral Rag Member but base not seen, in facies implying moderate but variable energy conditions; sandy and muddy ooidal limestone interbedded with ooidal grainstone. Wright and Cox, 2001, pp 173-179 
Reference Section  Helmsley Quarry, Helmsley, North Yorkshire: exposes full thickness of member at 6.5m thick unusually thin, in sandy ooidal facies, with calcareous sandstone beds, underlain by Middle Calcareous Grit, and overlain by Coral Rag Member. Wright, 1972, p 246 
Type Section  Whitewall Corner Quarry, Norton on Derwent, North Yorkshire: exposes (2009) 36 m of interbedded shelly coarse-grained ooid-grainstone and ooid-packstone/wackestone, base not seen, overlain non-sequentially by coralliferous limestone of Coral Rag Member Wright, 1972, pp 229, 252; Wright, 2009, p. 202, fig. 5 
Reference Section  Wath New Quarry, Hovingham, North Yorkshire: exposes (2006) full thickness of the Malton Oolite Member 33m thick: 16m of planar bedded, shelly, bioclastic, ooidal calcilutite, with thin interbeds of grey mudstone, overlain by 17m of cross-bedded, interbedded ooid-grainstone and shelly ooid-packstone/wackestone, with thin interbeds of grey mudstone. Underlain by fine-grained sandstone and mudstone of possible Middle Calcareous Grit Member, overlain non-sequentially by coralliferous limestone of Coral Rag Member. Wright, 2009, p. 204, fig. 5; Wright and Cox, 2001, pp 179-182 
Reference(s):
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. 
Wright, J K. 1972. The stratigraphy of the Yorkshire Corallian. Proceedings of the Yorkshire Geological Society, Vol. 39, 225-266. 
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.) 
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.] 
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. 
Fox-Strangways, C. 1892. The Jurassic Rocks of Britain, Vol.1. Yorkshire. Memoir of the Geological Survey of the United Kingdom. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E044 E052 E053 E054 E063