The BGS Lexicon of Named Rock Units — Result Details

Gault Formation
Computer Code: GLT Preferred Map Code: G
Status Code: Full
Age range: Albian Age (KA) — Albian Age (KA)
Lithological Description: Pale to dark grey or blue-grey clay or mudstone, glauconitic in part, with a sandy base. Discrete bands of phosphatic nodules (commonly preserving fossils), some pyrite and calcareous nodules. At Munday's Hill, Bedfordshire the base of the Gault Formation is brick-red mudstone called informally the "Cirripede Bed". In Norfolk, the Gault Formation becomes calcareous before passing northwards into the Hunstanton Formation ("Red Chalk"). In places thin, variable junction beds at the base include some limestones.
Definition of Lower Boundary: The base is an unconformity. There is a rapid transition from sands of the Lower Greensand Group and equivalents where these are present or a marked break where the basal Gault Formation rests on rocks down to Triassic in age. Beneath London the lower part of the Gault Formation is absent or severely attenuated over the London-Brabant Ridge (formed of Palaeozoic rocks). Generally the base of the Gault Formation is taken at the base of a phosphatic pebble bed or gritty mudstone where it overlies the Carstone in East Anglia, the Monk's Bay Sandstone Formation on the Isle of Wight or the Folkestone Formation of the Weald. Elsewhere in southern England the base of the Gault Formation rests on an unconformity and oversteps onto undivided Lower Greensand Group sandstones and ironstone, may overlie attenuated Wealden, and oversteps onto various units of the Jurassic. In the extreme west of the outcrop the overstep places the Gault Formation on Triassic mudstones and sandstones.
Definition of Upper Boundary: The top of the formation is a diachronous transition from mudstone into Upper Greensand Formation facies (glauconitic sand) westward of a line from Sevenoaks (Kent) to Lewes (Sussex). In eastern areas the upper boundary of the formation is the unconformable junction with the basal Grey Chalk Subgroup (argillaceous, glauconitic sandstone, chalky sandstone and sandy chalk, with common phosphatic nodules). In Cambridgeshire the mudstones of the Gault Formation are overlain at a sharp erosive junction by the strongly phosphatic sandstone of the Cambridge Greensand Member at the base of the Chalk Group (West Melbury Marly Chalk Formation).
Thickness: About 2m in north Norfolk, thickening southwards to 20m in Cambridgeshire, 60m in Bedfordshire, and 90 to 110m in the Weald (104m in the Glyndebourne Borehole TQ41SW/16 [TQ4420 1141]).
Geographical Limits: Extensive outcrop in eastern England from Norfolk, southwestwards across the East Midlands and Home Counties to Devon, in the Isle of Wight and around the margins of the the Weald.
Parent Unit: Selborne Group (SELB)
Previous Name(s): Gault (-2208)
Gault Clay (-2209)
Blue Marle (-3435)
Gault Clay Formation (-1565)
Golt (-934)
Blue Marl (-123)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Marham Borehole TF70NW/1 [7051 0803] (Gallois and Morter, 1982). The full thickness of the formation was cored between 33.43 and 45.03m depth. 
Reference Section  Mundford C Borehole TL79SE/13 [7670 9132] (Gallois and Morter, 1982). Full succession between 89.59 and 107.87m depth 
Type Section  Long regarded as Copt Point cliff section at Folkestone, Kent (Price, 1874; Topley, 1875; Jukes-Browne and Hill, 1900; Owen, 1971). Full succession visible. Divided into beds (I-XIII). See Smart et al. (1966). 
Reference Section  The three boreholes (1 to 3) at Selborne in Hampshire (SU73SW/22 [7320 3494], SU73SE/39 [7540 3435] and SU73SE/40 [7583 3400]). Boreholes together give a complete lower and upper Gault Formation succession (Hopson, Farrant and Booth, 2001). 
Reference Section  Gayton Borehole TF71NW/10 [7280 1974] (Gallois and Morter, 1982). The full succession was cored between 11.50 and 22.00m depth. 
Reference Section  The Arlesey Borehole (Arlesey Brickpit, SE Bedfordshire) TL13SE/45 [1887 3463]. The borehole shows a complete section through the preserved Gault Formation 15.45 to 72.96m depth (Hopson, 1992; Woods, Wilkinson and Hopson, 1995). 
Reference(s):
Jukes-Browne, A J and Hill, W. 1900. The Cretaceous Rocks of Britain. 1. Gault and Upper Greensand. Memoir of the Geological Survey of Great Britain. 
Hancock, J M (Editor). 1972. Cretace. Ecosse, Angleterre, Pays de Galles. Lexique Stratigraphique International, Vol.1, fascicule 3a XI. 
Owen, H G. 1971. Middle Albian stratigraphy in the Anglo-Paris basin. Bulletin of the British Museum (Natural History): Geology, Supp.8, 1-164. 
Hopson, P M, Farrant, A R and Booth, K A. 2001. Lithostratigraphy and regional correlation of the basal Chalk, Upper Greensand, Gault and Uppermost Folkestone formations (mid Cretaceous) from cored boreholes near Selborne, Hampshire. Proceedings of the Geologists' Association, Vol.112, 193-210. 
Smart, J G O, Bisson, G and Worssam, B C. 1966. Geology of the Country around Canterbury and Folkestone. Memoir of the Geological Survey of Great Britain, Sheets 289, 305 and 306 (England and Wales). 
Hailstone, J. 1816. Outlines of the geology of Cambridgeshire. Transactions of the Geological Society of London, Vol.3, 243-250. 
Hopson, P M. 1992. Geology of the Letchworth, north-west Hitchin and Holwell district, Hertfordshire. British Geological Survey Technical Report, WA/92/42. 
Price, F G H. 1874. On the Gault of Folkestone. Quarterly Journal of the Geological Society of London, Vol.30, 342-366. 
Rawson, P F, Curry, D, Dilley, F C, Hancock, J M, Kennedy, W J, Neale, J W, Wood, C J and Worrsam, B C. 1978. A correlation of Cretaceous rocks in the British Isles. Geological Society of London, Special Report No.9. 
Topley, W. 1875. The Geology of the Weald. Memoir of the Geological Survey of Great Britain. 
Owen, H G. 1972. The Gault and its junction with the Woburn Sands in the Leighton Buzzard area, Bedfordshire and Buckinghamshire. Proceedings of the Geologists' Association, Vol.83, 287-312. 
Owen, H G. 1992. The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment. Proceedings of the Geologists' Association, Vol.103, 83-110. 
Woods, M A, Wilkinson, I P and Hopson, P M. 1995. The stratigraphy of the Gault Formation (Middle and Upper Albian) in the BGS Arlesey Borehole, Bedfordshire. Proceedings of the Geologists' Association, Vol.106, 271-280. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E129 E145 E146 E160 E161 E162 E173 E175 E176 E187 E188 E189 E190 E203 E204 E205 E206 E207 E208 E219 E220 E221 E222 E225 E236 E237 E238 E239 E240 E252 E253 E254 E256 E257 E258 E259 E266 E267 E268 E269 E270 E271 E272 E273 E274 E281 E282 E283 E284 E285 E298 E300 E326 E327 E340 E341 E342 E343
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