The BGS Lexicon of Named Rock Units — Result Details

Lower Greensand Group
Computer Code: LGS Preferred Map Code: LGS
Status Code: Index Level
Age range: Aptian Age (KP) — Albian Age (KA)
Lithological Description: Mainly sands and sandstones (varying from well-sorted fine-grained to poorly sorted medium- to coarse-grained) with silts and clays in some intervals.
Definition of Lower Boundary: In southern England, erosional unconformity or disconformity at base of Atherfield Clay Formation: in most of area overlies Wealden Clay Formation, elsewhere Lower Greensand Group oversteps onto Jurassic rocks.
Definition of Upper Boundary: Base of Gault; specifically in the Wealden area, base of a short interval of condensed facies beds at the base of the silty clays of the Gault above the sands of the Folkestone Formation.
Thickness: c.250m in south-western Weald
Geographical Limits: As described, circum-Weald. Also developed in the Isle of Wight, and less well in Wiltshire to Bedfordshire, Norfolk, Dorset, Lincolnshire and Yorkshire.
Parent Unit: Not Applicable (-)
Previous Name(s): Lower Greensand (-1024)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Wealden area: see type sections for component parts: Atherfield Clay Formation, Hythe Formation, Sandgate Formation and Folkestone Formation. 
Reference(s):
Rawson, P F. 1992. Cretaceous. 355-388 in Duff, P McL D and Smith, A J (editors), Geology of England and Wales. [Geological Society: London.] 
Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E317 E332 E318 E333 E319 E334 E331 E328 E269 E254 E313 E266 E282 E298 E237 E173 E175 E187 E188 E189 E203 E204 E205 E236 E252 E253 E265 E219 E268 E271 E273 E274 E281 E284 E341 E342 E343
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