The BGS Lexicon of Named Rock Units — Result Details

Folkestone Formation
Computer Code: FO Preferred Map Code: F
Status Code: Full
Age range: Aptian Age (KP) — Albian Age (KA)
Lithological Description: In Sussex, Kent and Surrey the formation comprises medium- and coarse-grained, well-sorted cross-bedded sands and weakly cemented sandstones; elsewhere includes calcareous sandstones. There are no formal divisions in the Weald, but equivalent beds in the west are termed the Child Okeford Sand Member and the Bedchester Sands Member.
Definition of Lower Boundary: The base of the formation is the contact of sand or sandstone of the formation with underlying silty clay or clayey silt of the Marehill Clay Member (Sandgate Formation) or with a heterogeneous succession of clays, silts and sands (Sandgate Formation, undifferentiated). This boundary can be diffuse in places but is generally marked by a colour change.
Definition of Upper Boundary: The upper boundary is generally placed at the upward disappearance of sand at the base of the Gault Formation. In places the top is at the base of a thin pebbly sandy clay condensed succession at the base of the Gault Formation. In Sussex the top of the formation is at the base of the "Iron Grit" (a hard, pebbly, limonitic, coarse-grained sandstone) (see Casey, 1961).
Thickness: Between 0.5 and 80m.
Geographical Limits: West Sussex and southeast Hampshire; otherwise circum-Weald.
Parent Unit: Lower Greensand Group (LGS)
Previous Name(s): Folkestone Beds (-1545)
Folkestone Sands (-2190)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  East Cliff, Folkestone, Kent. Almost continuous section showing the Formation and the lowest beds of the overlying Gault Formation. The lower 15 feet (4.57m) of the formation are normally obscured See Smart et al. (1966, p.94). 
Reference(s):
Young, B and Lake, R D. 1988. Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey, sheets 318 and 333. 
Anderson, I D. 1986. The Gault Clay - Folkestone Beds junction in West Sussex, southeast England. Proceedings of the Geologists' Association, Vol.97(1), 45-58. 
Drew, F. 1864. The geology of the country between Folkestone and Rye, including the whole of Romney Marsh (Sheet 4). Memoir of the Geological Survey of the United Kingdom. 
Casey, R. 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
Bristow, C R and Wyatt, R J. 1983. Geological notes and local details for 1:10,000 Geological sheets TQ01nW, NE, SW and SE (Pulborough and Storrington). [Keyworth: British Geological Survey.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E271 E272 E284 E285 E286 E287 E288 E289 E300 E301 E305 E317 E318 E332 E333
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