The BGS Lexicon of Named Rock Units — Result Details

Mulgrave Shale Member

Computer Code: MULG Preferred Map Code: Mu
Status Code: Full
Age range: Toarcian Age (JT) — Toarcian Age (JT)
Lithological Description: Mudstone, dark grey, bituminous and pyritic, with common layers of grey calcareous concretions, ovoid and spherical and ranging up to 4.5 m in diameter, particularly in the lower third (the Jet Rock) which also hosts the horizon bearing the black, highly compressed fossil wood (jet); similar concretions are also present at the top of the upper third (Bituminous Shales); fossils including ammonites and belemnites common throughout.
Definition of Lower Boundary: Conformable: base of bituminous mudstone with large concretions resting upon non-bituminous shaly mudstone (Grey Shale Member). Bed 33 on Bed 32 at Hawsker Bottoms and Port Mulgrave (bed numbers of Howarth, 1955).
Definition of Upper Boundary: Conformable: base of non-bituminous grey shaly mudstone (Alum Shale Member) resting upon dark grey bituminous mudstone with a double layer of sideritic concretions (Ovatum Bed). Bed 49 on Bed 48 at Hawsker Bottoms and Whitby (bed numbers of Howarth, 1955).
Thickness: 31m thick on the Yorkshire coast, thins west and south to between 23 and 25m (Brown Moor and Felixkirk boreholes)(Gaunt et al., 1980; Powell et al., 1992).
Geographical Limits: Cleveland Basin as far south as Acklam area, becoming indistinguishable southwards (see Supplementary Information).
Parent Unit: Whitby Mudstone Formation (WHM)
Previous Name(s): Jet Rock Plus Bituminous Shales (-2331)
Jet Rock Formation (-1713)
Jet Rock Series (-4209)
Jet Rock Member (-336)
Alternative Name(s): none recorded or not applicable
Reference Section  Upper part exposed in cliffs and foreshore at Saltwick Nab east of Whitby, North Yorkshire coast, up to about 28m seen. Beds 35 to 48 of Howarth (1955). Simms et al., 2004, pp 299-304. 
Type Section  Fully exposed in continuous foreshore at Port Mulgrave, North Yorkshire coast, about 31m thick. Beds 33 to 48 of Howarth (1955). Rawson and Wright, 1995, pp 203-206; Simms et al., 2004, pp 281-293. 
Reference Section  Fully exposed in cliffs and foreshore east of Hawsker Bottoms, North Yorkshire coast, about 30m thick. Beds 33 to 48 of Howarth (1955). Simms et al., 2004, pp 262-271. 
Simms, M J, Chidlaw, N, Morton, N, and Page, K N. 2004. British Lower Jurassic Stratigraphy. Geological Conservation Review Series. No. 30. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
Howarth, M K, 1980, Toarcian correlation chart, in Cope, J C W (editor). 1980. A correlation of the Jurassic rocks of the British Isles. Part One: Introduction and Lower Jurassic. Geological Society of London Special Report. No. 14. 
Powell, J H, 1984. Lithostratigraphic nomenclature of the Lias Group in the Yorkshire Basin. Proceedings of the Yorkshire Geological Society, Vol.45, p.51-57. 
Hemingway, J E. 1974. Jurassic. 161-233 in Rayner, D H and Hemingway, J E (eds), The geology and mineral resources of Yorkshire. (Leeds: Yorkshire Geological Society.) 
Rawson, P F and Wright, J K (eds). 1992. The Yorkshire Coast. Geologists' Association Guide, No.34. 2nd Edition, 117pp. (Ongar: PSS Group.) 
Fox-Strangways, C and Barrow, G, 1915. The geology of the country between Whitby and Scarborough (2nd edition). Memoir of the Geological Survey of the United Kingdom. 
Howarth, M K, 1955. Domerian of the Yorkshire coast. Proceedings of the Yorkshire Geological Society, Vol.30, 147-175. 
Powell, J H, Cooper, A H C and Benfield, A C. 1992. Geology of the country around Thirsk. Memoir of the British Geological Survey, Sheet 52 (England and Wales). 
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.) 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E042 E043 E044