The BGS Lexicon of Named Rock Units — Result Details

Long Nab Member

Computer Code: LNAB Preferred Map Code: notEntered
Status Code: Full
Age range: Bajocian Age (JB) — Bathonian Age (JN)
Lithological Description: It comprises grey, laminated mudstones and siltstones with yellow-grey, fine- to medium-grained, planar bedded and cross-stratified sandstones. Trough cross-bedded channel-fill sandstones are also present. Plant fragments, plant rootlets and drifted wood casts are common, together with occasional, thin coals, and grey mudstone seatearths. Dinosaur footprints are occasionally present.
Definition of Lower Boundary: The lower boundary is conformable or disconformable at the gradational upward transition from white or grey, fine- to medium-grained cross-bedded sandstone of the Moor Grit Member, to the predominantly level-bedded siltstone, mudstone or thin, cross-laminated sandstone with plant fragments of the Long Nab Member (Nami and Leeder, 1978; Livera and Leeder, 1981; Powell et al., 1992).
Definition of Upper Boundary: The upper boundary is conformable or disconformable, at the boundary between siltstone, mudstone or cross-bedded sandstone with plant fragments of the Long Nab Member (Scalby Fm.) and the Cornbrash Formation, which at Cayton Bay [TA 078 841], comprises red-brown, sandy, nodular, bioturbated limestone with oysters and other bivalves; u-shaped burrows extend down from the base of the Cornbrash Formation into the underlying grey siltstone and silty sandstone of the Scalby Formation (Wright, 1977). Inland in the Hambleton Hills and Howardian Hills, the Cornbrash Formation (limestone) is generally absent (Powell et al., 1992, p.53) and the upper boundary is taken at the base of the yellow-brown, calcareous medium-grained sandstone with bivalves (Kellaways Rock Member, Osgodby Formation). The Kellaways Rock Memmber is referred to as the Redcliff Rock Member by Page (1989).
Thickness: It ranges in thickness from 23 to 28 m on the North Yorkshire Coast 24 to 33 m inland in the Hambleton Hills. It thins south-westwards towards the Market Weighton High and is between 5 to 10 m thick in the Howardian Hills.
Geographical Limits: North Yorkshire Moors, Cleveland Hills, Hambleton Hills and Howardian Hills, and is well exposed in several coastal cliff sections (Scalby Cliff) between Long Nab [TA 028 943] and Scalby Ness [TA 037 907], 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 by the Redbourne Group (Gaunt et al., 1992). Offshore, the formation 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): Upper Deltaic Series (Part) (-2909)
Upper Estuarine Series (Part) (-1036)
Level Bedded Unit (-4766)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Coastal cliff section (Scalby Cliff) near Scalby Mills, north of Scarborough, between Long Nab [TA 028 943], Scalby Ness [TA 037 907] and southwards to Castle Hill [TA 048 893]. Along this 10.5 km section, it consists of grey mudstone, siltstone and sandstone, with local channel sandstone bodies. Plant fragments, rootlet horizons and drifted logs are common in the upper member, and thin coals are locally present. Dinosaur footprints are occasionally present. The lower gradational boundary with the underlying Moor Grit Member is well exposed north of Long Nab [TA 028 943]. The upper boundary with the overlying Cornbrash Formation is not exposed until farther south, on the north side of Castle Hill [TA 048 893], Scarborough (Fox-Strangways, 1892). A better, intermittently exposed upper boundary at Cayton Bay is given in the reference section, below. 
Reference Section  Reference section for the upper boundary on the south side of Cayton Bay, south of Scarborough. Conformable or disconformable, at the boundary between siltstone, mudstone or cross-bedded sandstone with plant fragments of the Long Nab Member (Scalby Fm.) and the overlying Cornbrash Formation, which at Cayton Bay [TA 078 841], comprises red-brown, sandy, nodular, bioturbated limestone with oysters and other bivalves; u-shaped burrows extend down from the base of the Cornbrash Fm. into the underlying grey siltstone and silty sandstone of the Scalby Formation (Wright, 1977). 
Reference(s):
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). 
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. 
Black, M. 1929. Drifted plant-beds of the Upper Estuarine Series of Yorkshire. Quarterly Journal of the Geological Society of London, 85, 389-437. 
Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B, and Riding, J B. 1993, 3. Jurassic of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.). Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham, viii + 219 p. 
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]. 
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.) 
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. 
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. 
Cope, J C W, Duff, K L, Parsons, C F, Torrens, H S, Wimbledon, W A and Wright, J K. 1980. A correlation of Jurassic rocks in the British Isles. Part 2: Middle and Upper Jurassic. Geological Society of London Special Report, 15, 73pp. 
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. 
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. 
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. 
Wright, J K. 1977. The Cornbrash Formation (Callovian) in North Yorkshire and Cleveland. Proceedings of the Yorkshire Geological Society, Vol.41, 325-346. 
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.) 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E034 E035 E043 E044 E052 E054 E063