The BGS Lexicon of Named Rock Units — Result Details

Portland Sand Member (Wiltshire, Oxfordshire And Buckinghamshire) [Use Not Recommended In BGS: Prefer POSA]

Computer Code: PSND Preferred Map Code: PIS
Status Code: Full
Age range: Tithonian Age (JI) — Tithonian Age (JI)
Lithological Description: Calcareous sandstones and sands, commonly glauconitic (Glauconitic Beds) and conglomeratic sandstones, sands, marls and limestones (Upper Lydite Bed).
Definition of Lower Boundary: Conglomeratic and glauconitic coarse-grained sand, sandstone and limestone (Upper Lydite Bed) resting non-sequentially on mudstones, siltstones or fine-grained argillaceous sands and sandstones of the Upper Kimmeridge Clay.
Definition of Upper Boundary: Either seen as a transition from calcareous sandstones and sands, commonly glauconitic (Glauconitic Beds), to limestone of Portland Stone Member, which is probably diachronous, or as a sharp, non-conformable junction with generally non-calcareous and commonly ferruginous sands and sandstones of the Lower Greensand, or Whitchurch Sand Formations, or by calcareous mudstones of the Gault Formation.
Thickness: Up to 6 m thick.
Geographical Limits: Outliers from Swindon to Aylesbury in north Wiltshire, Oxfordshire and Buckinghamshire, and possiblly an outlier in the Vale of Pewsey near Devizes, though this is currently rather poorly known (see Wimbledon, 1980). A separate description applies to the Portland of the Vale of Wardour in south Wiltshire or Dorset.
Parent Unit: Portland Formation (Wiltshire, Oxfordshire And Buckinghamshire) [Use Not Recommended In BGS: Prefer PL] (PLND)
Previous Name(s): Portland Sand (-2373)
Upper Lydite Bed (-4851)
Glauconitic Beds (-4273)
Alternative Name(s): none recorded or not applicable
Type Section  BGS Hartwell Borehole, 12.19 - 17.95 m depth. Cox, Gallois and Sumbler, 1994; Horton et al., 1995. 
Reference Section  Swindon Old Town Railway Cutting. Wimbledon, 1976. 
Type Area  Thame to Aylesbury area. 1:50 000 Sheet 237. 
Wimbledon, W A. 1976. The Portland Beds (Upper Jurassic) of Wiltshire. Wiltshire Archaeological and Natural History Magazine, Natural History, Vol.71, 3-11. 
Horton, A, Sumbler, M G, Cox, B M and Ambrose, K, 1995. Geology of the country around Thame. Memoir of the British Geological Survey, Sheet 237 (England and Wales). 
Wimbledon, W A. 1980. Portlandian correlation chart. 85-93 in Cope, J C W (Editor), A correlation of the Jurassic rocks of the British Isles. Part Two: Middle and Upper Jurassic. Geological Society of London Special Report, No.15. 
Cox, B M, Gallois, R W and Sumbler, M G. 1994. The stratigraphy of the BGS Hartwell Borehole, near Aylesbury, Buckinghamshire. Proceedings of the Geologists' Association, Vol. 105, 209-224. 
Cox, B M, 1996, Portland and Purbeck Formations. In: British Regional Geology: London and the Thames Valley. Fourth Edition. Sumbler, M G, (Editor), 58-60. (London HMSO.) 
Wimbledon, W A and Cope, J C W. 1978. The ammonite faunas of the English Portland Beds and the zones of the Portlandian Stage. Journal of the Geological Society of London, Vol.135, 183-190. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E219 E220 E237 E252 E282