The BGS Lexicon of Named Rock Units — Result Details

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

Computer Code: PSTN Preferred Map Code: PlS
Status Code: Full
Age range: Tithonian Age (JI) — Tithonian Age (JI)
Lithological Description: Variable sandy marine limestones commonly with large and robust molluscan macrofauna, such as the Aylesbury Limestone, Rubbly Limestone, Cockly Bed, Creamy Limestone and Town Gardens Limestone) and variable calcareous sands and sandstones, generally non-glauconitic such as the Crendon Sand, Swindon Sand and Swindon Sandstone.
Definition of Lower Boundary: Upward transition from variable calcareous and glauconitic sand or sandstone such as the Portland Sand Member, to variable sandy limestone.
Definition of Upper Boundary: Upward change from fully marine limestones with large molluscan fossils of Portland Stone Member to lagoonal fine-grained limestones and marls of Purbeck Formation (the base of which is commonly Marked either by laminated, ostracod-bearing 'Pendle' or oyster-bearing marl, or by a sharp non-sequential contact with overlying, generally non-calcareous and commonly ferruginous sands and sandstones of the Lower Greensand or Whitchurch Sand Formation, or by calcareous mudstones of the Gault Formation.
Thickness: Up to, and locally greater than 11 m thick.
Geographical Limits: Outliers from Swindon to Aylesbury, in north Wiltshire, Oxfordshire and Buckinghamshire, and possibly 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 in the Vale of Wardour, south Wiltshire andf Dorset.
Parent Unit: Portland Formation (Wiltshire, Oxfordshire And Buckinghamshire) [Use Not Recommended In BGS: Prefer PL] (PLND)
Previous Name(s): Portland Stone [Obsolete Code: Use POST] (PLST)
Alternative Name(s): none recorded or not applicable
Type Section  BGS Hartwell Borehole, 5.16 - 12.19 m. depth. Cox, Gallois and Sumbler, 1994; Horton et al., 1995. 
Reference Section  Town Gardens Quarry, Swindon. Wimbledon, 1976. 
Reference Section  Bugle Pit, Hartwell. 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. 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. 
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. 
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. 
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). 
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.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E219 E220 E237 E252 E282