The BGS Lexicon of Named Rock Units — Result Details

Frome Clay Formation

Computer Code: FRC Preferred Map Code: FC
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Silicate-mudstone, grey, blue grey and olive-grey, calcareous in parts, with minor generally fine-grained limestone units. Highly fossiliferous and/or bioturbated at some levels. A unit of between five and twenty 0.1m-thick muddy, shelly, bioturbated limestone beds interbedded with 0.3m-thick mudstone beds is developed at the base and termed the Wattonensis Limestone Member, which is poorly developed around Frome, but thickens south to the Dorset coast and offshore. Above it in Dorset, oyster-rich mudstone beds are developed at two levels.
Definition of Lower Boundary: The base of the Wattonensis Limestone Member, a thin unit (3 to 4m) of interbedded limestone and mudstone, resting on calcareous mudstone of the Fuller’s Earth Formation. Base defined by an increase in shell-detritus in the calcareous mudstone.
Definition of Upper Boundary: The base of the Boueti Bed (Forest Marble Formation) a thin shell-fragmental muddy limestone with abundant Goniorhynchia boueti overlying silicate mudstone of the Frome Clay Formation, which may contain burrows.
Thickness: 20 to 50m in Wiltshire and Somerset, 45 to 70m in Dorset (see Bristow et al. 1995).
Geographical Limits: From Norton St Philip [ST 76 56], near Bath, Somerset where passes north into ooid limestone of Chalfield Oolite Formation, south to Dorset coast, passing east at depth in western Hampshire into limestone (?Chalfield Oolite Formation) of Wessex Basin (Wyatt, 2011). Present in offshore English Channel south of the Hampshire-Dieppe High (Hamblin et al., 1992).
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Fuller's Earth (-2180)
Upper Fuller'S Earth (-5116)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Baggridge No.2 Borehole ST75NW/23, 26.25 to 47.82 m (Penn, I E and Wyatt, R J, 1979). Penetrated full thickness comprising variably calcareous mudstone with minor limestone beds; Wattonensis Limestone Member not developed at base here. North of here, within 1 to 3 km, the formation passes laterally into the limestone beds of the Chalfield Oolite Formation, and the calcareous nature of some of the beds in the borehole shows this lithological change. 
Reference Section  Purse Caundle Borehole ST71NW/7, 0 to 12.48 m depth (Barton, C M, et al, 1993). Penetrated lower part comprising 2.91m of interbedded limestone and mudstone of the Wattonensis Limestone Member at base overlain by 9.5m of olive-grey calcareous mudstone, variably bioclastic with a fauna dominated by bivalves. 
Type Section  Frome (Gibbet Hill) Borehole ST74NE/3, 22.56 to 52.63 m depth (Penn, I E and Wyatt, R J, 1979). Penetrated full thickness of 30.07m, comprising variably calcareous mudstone with minor limestone beds; Wattonensis Limestone Member not developed at base here. 
Reference Section  Winterborne Kingston Borehole SY89NW/1, 732.7 to 793.0 m depth (Penn, I E, 1982). Penetrated full thickness, comprising 4.4m of interbedded limestone and mudstone of the Wattonensis Limestone Member at base overlain by 5.4m of dark grey fissile mudstone, overlain by 50.5m of grey calcareous mudstone. 
Reference(s):
Barton, C M, Ivimey-Cook, H C, Lott, G K, and Taylor, R T. 1993. The Purse Caundle Borehole, Dorset: stratigraphy and sedimentology of the Inferior Oolite and Fuller's Earth in the Sherborne area of the Wessex Basin. British Geological Survey Research Report, SA/92/01. 
Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M, Ivimey-Cook, H C, and Taylor, R T. 1995. Geology of the country around Shaftesbury. Memoir of the British Geological Survey, Sheet 313 (England and Wales). 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Cope, J C W (Editor) 1980b. A correlation of Jurassic rocks in the British Isles. Part Two: Middle and Upper Jurassic. Geological Society of London Special Report, No.15 
Penn, I E and Wyatt, R G, 1979. The stratigraphy and correlation of the Bathonian strata of the Bath-Frome area. Report of the Institute of Geological Sciences, No.78/22, 23-88. 
Penn, I E, 1982. Middle Jurassic stratigraphy and correlation of the Winterborne Kingston Borehole, Dorset. 53-76 in Rhys, G H, Lott, G K and Calver, M A (editors), The Winterborne Kingston Borehole, Dorset, England. Report of the Institute of Geological Sciences, No.81/3. 
Bourne, J C. 1846. The history and description of the Great Western Railway. (London.) 
Wyatt, R J. 2011. A gamma-ray correlation of boreholes and oil wells in the Bathonian Stage succession (Middle Jurassic) of the Wealden Shelf subcrop. British Geological Survey Open Report, OR/11/048. 
Palmer, C P. 2005. Oyster lumachelles in the Fleet, Dorset. Proceedings of the Dorset Natural History and Archaeological Society, Vol. 127, 87-94. 
Barron, A J M, Lott, G K, and Riding, J B. 2012. Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report RR/11/06. 
Hamblin, R J O, Crosby, A, Balson, P S, Jones, S M, Chadwick, R A, Penn, I E, and Arthur, M J. 1992. The geology of the English Channel. British Geological Survey United Kingdom Offshore Regional Report. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E281 E297 E313 E327 E341 E342 E343