The BGS Lexicon of Named Rock Units — Result Details

Moor Grit Member

Computer Code: MRG Preferred Map Code: notEntered
Status Code: Full
Age range: Bajocian Age (JB) — Bajocian Age (JB)
Lithological Description: The Moor Grit Member is dominated in coastal exposures by grey, medium- to coarse-grained, occasionally pebbly, trough cross-bedded sandstone, with thin siltstone and mudstone beds; plant fragments and fossil wood casts are common . Inland, in the Hambleton Hills (Powell et al., 1992) it consists of grey to white, fine-grained, orthoquartzitic sandstone, with low-angle cross stratification and planar bedding.
Definition of Lower Boundary: The lower boundary is disconformable or unconformable, at the abrupt upward transition from grey, shelly mudstone or shelly sandstone of the Scarborough Formation to grey, cross-bedded and planar laminated sandstone with occasional plant fragments of the Moor Grit Member (Nami and Leeder, 1978; Gowland and Riding, 1991; Powell et al., 1992). The base is often a scoured, erosional surface.
Definition of Upper Boundary: The upper boundary is conformable or disconformable, at the boundary between white or grey, fine- to medium-grained cross-bedded sandstone (Moor Grit Member), and predominantly level-bedded siltstone, mudstone or thin, cross laminated sandstone with plant fragments of the Long Nab Member (Nami and Leeder, 1979).
Thickness: Between 8 to 12 m thick on the North Yorkshire coast (Hemingway, 1974); 8 - 15 m in the Hambleton Hills in the west of the outcrop (Powell et al., 1992); in the Howardian Hills it thins southwards to about 1 m thick (J Ford, pers. comm. 2008)
Geographical Limits: North Yorkshire Moors, Cleveland Hills, Hambleton Hills and Howardian Hills, and is well exposed in several coastal cliff sections between Hundale Point [TA 025 948] and Long Nab [TA 031 940], and south of Scarborough between South Bay [TA 046 875] and White Nab [TA 058 864] (Black, 1929; Hemingway and Knox, 1973; Nami and Leeder, 1978). Equivalent strata in Humberside and Lincolnshire are represented, in part, by the Redbourne Group (Gaunt et al., 1992). Offshore, the member is equivalent, in part, to the Hudleston Formation of the West Sole Group (Lott and Knox, 1994).
Parent Unit: Scalby Formation (SCY)
Previous Name(s): Cross-Bedded Series (-1711)
Alternative Name(s): Moor Grit
Stratotypes:
Type Section  Coastal cliff section between Hundale Point [TA 025 948] and Long Nab [TA 028 943], where the boundary between the shelly mudstone of the underlying Scarborough Formation is marked by an erosional disconformity/unconformity with the Moor Grit Member (c. 15 m thick). The latter consists of medium- to coarse-grained, trough cross-bedded sandstone with pebbly laminae; plant fragments are common, along with casts and moulds of drifted logs. Laterally accreted channel-fill bedforms are common (Black, 1929; Hemingway and Knox, 1973; Hemingway, 1974; Nami and Leeder, 1978; Leeder and Nami, 1979). 
Reference(s):
Black, M. 1929. Drifted plant-beds of the Upper Estuarine Series of Yorkshire. Quarterly Journal of the Geological Society of London, 85, 389-437. 
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.) 
Butler, N, Charnock, M A, Hager, K O and Watkins, C A. 2005. The Ravenscar Group: a coeval analogue for the Middle Jurassic reservoirs of the North Sea and offshore Mid-Norway. 43-53 in Powell, A J and Riding, J B (eds), Recent Developments in Applied Biostratigraphy. The Micropalaeontological Society, Special Publications. 
Hancock, N J and Fisher, M J. 1981. Middle Jurassic North Sea deltas with particular reference to Yorkshire. 186-195 in Illing, L V and Hobson, G D (eds), Petroleum geology of the continental shelf of north-west Europe. (London: Institute of Petroleum.) 
Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. [British Geological Survey, Nottingham]. 
Fisher, M J and Hancock, N J. 1985. The Scalby Formation (Middle Jurassic, Ravenscar Group) of Yorkshire: reassessment of age and depositional environment. Proceedings of the Yorkshire Geological Society, Vol.45, 293-298. 
Fox-Strangways, C. 1892. Jurassic rocks of Britain, Vols 1 and 2, Yorkshire. Memoir of the Geological Survey of Great Britain. 
Leeder, M R and Nami, M. 1979. Sedimentary models for the non-marine Scalby Formation (Middle Jurassic) and the evidence for late Bajocian/Bathonian uplift of the Yorkshire Basin. Proceedings of the Yorkshire Geological Society, Vol.42, 461-482. 
Riding, J B and Wright, J K. 1989. Palynostratigraphy of the Scalby Formation (Middle Jurassic) of the Cleveland Basin, north-east Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.47, 349-354. 
Nami, M and Leeder, M R. 1978. Changing channel morphology and magnitude in the Scalby Formation (M. Jurassic) of Yorkshire, England. In: Miall, A D (Ed.), Fluvial sedimentology. Memoir of the Canadian Society of Petroleum Geologists, No.5. 
Livera, S E and Leeder, M R. 1981. The Middle Jurassic Ravenscar Group (Deltaic Series) of Yorkshire: recent sedimentological studies as demonstrated during a field meeting 2/3 May, 1980. Proceedings of the Geologists' Association, Vol.92, 241-250. 
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). 
Gowland, S and Riding, J B. 1991. Stratigraphy, sedimentology and palaeontology of the Scarborough Formation (Middle Jurassic) at Hundale Point, North Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.48, 375-392. 
Hemingway, J E and Knox, R W O'B. 1973. Lithostratigraphical nomenclature of the Middle Jurassic strata of the Yorkshire Basin of north-east England. Proceedings of the Yorkshire Geological Society, Vol.39, 527-535. 
Knox, R W O'B, Howard, A S, Powell, J H and van Buchem, F S P. 1991. Lower and Middle Jurassic sediments of the Cleveland Basin N.E. England: Shallow marine and paralic facies seen in their sequence stratigraphic context. Field Excursion Guide, No.5; 13th International Sedimentological Congress, Nottingham, UK. 1990. 66pp. 
Gaunt, G D, Fletcher, T P and Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 172pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E043