The BGS Lexicon of Named Rock Units — Result Details

Bargate Sandstone Member

Computer Code: BT Preferred Map Code: Bt
Status Code: Full
Age range: Aptian Age (KP) — Aptian Age (KP)
Lithological Description: In the Guildford district the Member comprises buff to brown, gritty to ferruginous, cemented, cross-bedded, coarse-grained sandstone with beds of pale grey calcareous sandstone. Locally a pebble bed occurs at the base, with clasts of Hythe Formation, glauconite pebbles, quartz granules, brown phosphatic pebbles and pebbles of Jurassic limestone. Locally, e.g. Milford Bypass [SU 9435 4413] the member is weakly calcareous and chert beds occur, including one at the base. Hard, calcareous sandstone doggers (Bargate Stone) have also been recorded near the top of the unit around Dorking. In the northeastern part of the Alresford district it consists of friable, calcareous, glauconitic, fine- to medium-grained sandstones and cemented flagstones.
Definition of Lower Boundary: The lower boundary is placed at a burrowed erosion surface where pebbly sand rests on pale grey, well-sorted, fine- to medium-grained, weakly cemented sandstone of the Hythe Formation (Ellison et al., 2002). Locally, in the Alresford district, the member interdigitates with pebbly, glauconite- and limonite-rich clayey sand of the Rogate Member (Sandgate Formation) (Farrant, 2002).
Definition of Upper Boundary: In the Alresford district the upper boundary is characterised by an upsection change from brown, friable, calcareous, glauconitic sandstone, pebbly in part [Farrant, 2002] to grey, friable, well-sorted, fine-grained, glauconitic, weakly cross-bedded sandstone of the Pulborough Sandrock Member. In the Guildford district the brown, gritty, ferruginous, cemented, cross-bedded sandstone with beds of pale grey, calcareous sandstone (Ellison et al., 2002)are overlain by the argillaceous silts and fine- to medium-grained sandstones of the Sandgate Formation.
Thickness: To 35m in the Alresford district and to 20m in the Guildford district.
Geographical Limits: Restricted to the Alresford and Guildford districts. It forms a broad plateau south and west of Godalming [SU 95 43]. There are small outliers near Shere [TQ 0780 4730] and Abinger [TQ 1020 4680]. It is discontinuous around Albury Heath [TQ 058 466], Blackheath [TQ 038 464] and Farley Heath [TQ 046 430] and it is restricted to the northeastern part of the Alresford district.
Parent Unit: Sandgate Formation (SAB)
Previous Name(s): Bargate Formation (-2646)
Bargate Beds (-1401)
Bargate Member (-3878)
Alternative Name(s): Bargate Member Of The Sandgate Formation
Stratotypes:
Reference Section  Milford Bypass road cutting. This exposure shows "up to 7m of cross-bedded friable sandstone, weakly calcareous in places, with chert beds up to 0.3m thick at 1 to 2m intervals and a prominent 0.5m-thick weakly calcareous chert bed at the bottom" (Ellison et al. 2002). 
Type Section  Blackheath Lane. Albury. Dines and Edmunds, 1929; Kirkaldy, 1933. The Bargate Sandstone Member has "a slight southerly dip, and [the beds] are well developed being about 30 ft. thick"; and is "well exposed in the lane sides from the top of the hill almost to the stream running northwest from Brook" (Dines and Edmunds, 1929). 
Reference(s):
Dines, H G and Edmunds, F H. 1929. The Geology of the country around Aldershot and Guildford. Memoir of the Geological Survey of Great Britain, Sheet 285. [London: HMSO.] 
Murchison, R I, 1826. Geological Sketch of the North-west extremity of Sussex, and the adjoining parts of Hants and Surrey. Transactions of the Geological Society of London, (2), Vol.2, pp.97-107. 
Kirkaldy, J F. 1933. The Sandgate Beds of the Western Weald. Proceedings of the Geologists' Association, Vol.44, 270-311. 
Lake, R D and Shephard-Thorn, E R. 1985. The stratigraphy and the geological structure of the Hog's Back, Surrey and adjoining areas. Proceedings of the Geologists' Association, Vol.96, 7-21. 
Bristow, C R and Wyatt, R J. 1983. Geological notes and local details for 1:10 000 sheets TQ01NW, NE, SW and SE (Pulborough and Storrington). British Geological Survey Technical Report, WA/VG/83/03. 
Ellison, R A, Williamson, I T and Humpage, A J. 2002. Geology of the Guildford district - a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 Sheet 285 Guildford (England and Wales). 
Farrant, A R. 2002. Geology of the Alreford district - a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 sheet 300 Alresford [England and Wales]. 30pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E285 E300