The BGS Lexicon of Named Rock Units — Result Details

Gristhorpe Member

Computer Code: GRPE Preferred Map Code: notEntered
Status Code: Full
Age range: Bajocian Age (JB) — Bajocian Age (JB)
Lithological Description: Grey mudstone, yellow-grey siltstone and yellow-weathering, fine- to coarse-grained sandstone (fluvial, fluvio-deltaic and paralic lithofacies). Sandstones are commonly cross-bedded with sharp erosional bases and channel-fill bedforms. Thin coal seams, seatearth mudstone and nodular sideritic ironstone beds are present locally. Plant fragments and plant rootlets are common in some beds.
Definition of Lower Boundary: The lower boundary is conformable, or disconformable, and taken at the abrupt transition from marine strata (Lebberston Member) comprising pale grey, shelly ooidal cross-bedded limestone ("Whitwell Oolite" facies; Howardian Hills [SE 72 65]) or yellow, shelly calcareous cross-bedded sandstone with bivalves ("Millepore Bed" facies; Yons Nab [TA 084 844], south of Scarborough) to sandstone, siltstone and mudstone with plant remains (Gristhorpe Member).
Definition of Upper Boundary: The upper boundary is conformable, or disconformable, and taken at the abrupt upward transition from plant debris-rich, mudstone with plant rootlets, or cross-bedded sandstone of the upper part of the Gristhorpe Member (Cloughton Formation) to well laminated calcareous mudstone, or grey argillaceous limestone of the Scarborough Formation (Bate, 1965, p.83; Parsons, 1977; Gowland and Riding, 1991; Powell et al., 1992).
Thickness: Up to 30m on the North Yorkshire coast; thins to the southwest to about 20m in the Hambleton Hills and about 10m in the Howardian Hills.
Geographical Limits: North York Moors and Howardian Hills; well exposed in several coastal cliff sections between Ravenscar [NZ 981 019] and Cloughton Wyke [TA 024 949], and south of Scarborough at Gristhorpe Bay between Low Red Cliff [TA 080 842] and Yons Nab [TA 085 841] (White and Romano, 2006; Fig.19.2). Offshore, the formation is equivalent, in part, to the Wroot Formation of the West Sole Group (Lott and Knox, 1994). Where the marine Lebberston Member (Cloughton Formation) is absent (generally in the north of the Cleveland Basin) the non-marine strata (Sycarham and Gristhorpe members) are termed Cloughton Formation (undivided).
Parent Unit: Cloughton Formation (CLH)
Previous Name(s): Middle Deltaic Series (-3938)
Middle Estuarine Series (-3939)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Well exposed section in Gristhorpe Bay, near Scarborough, designated by Hemingway and Knox (1973) and described in more detail by Whyte and Romano (2006; 178-182). The Gristhorpe Member is well seen between [TA 083 843] and [TA 085 842] where it consists of interbedded grey mudstone and siltstone and yellow weathering, fine- to medium-grained, cross-bedded sandstone; plant remains and rootlets are common at some levels, especially in the mudstone and level-bedded sandstones (e.g. the informal Gristhorpe Plant Bed; Harris, 1953). Cross-bedded, channel sandstones commonly have sharp erosive bases, and laterally accreted bedforms. The term "Hawsker Member" (Hemingway and Knox, 1974) was proposed by these authors for the non-marine strata (c.f. Cloughton Formation) where the marine Lebberston Member is absent (generally in the north of the Cleveland Basin). The term "Hawsker Member" is redundant because the non-marine strata (Sycarham and Gristhorpe members) are represented by the Cloughton Formation (undivided). 
Reference(s):
Hemingway, J E. 1949. A revised terminology and subdivision of the Middle Jurassic rocks of Yorkshire. Geological Magazine, Vol.86, 67-71. 
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]. 
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. 
Whyte, M A and Romano, M. 2006. Middle-Upper Jurassic sequence between Cayton Bay and Yons Nab. 174-182 in Scrutton, C T and Powell, J H (eds), Yorkshire Rocks and Landscapes - A Field Guide, 3rd Edition. (Leeds: Yorkshire Geological Society.) 
Bate, R H. 1965. Middle Jurassic ostracoda from the Grey Limestone Series, Yorkshire. Bulletin of the British Museum (Natural History), Geology, Vol.11, 75-133. 
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.) 
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. 2000. The Yorkshire Coast. Geologists' Association Guide No.34. (London: The Geologists' Association.) 130pp. 3rd Edition. 
Harris, T M. 1953. The geology of the Jurassic flora of Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.29, 63-71. 
Parsons, C F. 1977. A stratigraphic revision of the Scarborough Formation. Proceedings of the Yorkshire Geological Society, Vol.41, 203-222. 
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. 
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:
E035 E044 E053 E054 E063