The BGS Lexicon of Named Rock Units — Result Details

Bampton Limestone Formation [Obsolete Code: Use BPLM]

Computer Code: BPM Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Visean Stage (CV) — Visean Stage (CV)
Lithological Description: Thin- to medium-bedded limestones, cherts, siliceous radiolarian mudstones (termed cherts in some literature) and mudstones. The limestones are locally partly silicified. The proportion of limestone, chert and mudstone varies vertically allowing a threefold division in the Bampton area; elsewhere these divisions have not been proved and there is evidence that north of Bampton the Formation is dominated by mudstones and cherts. At the base, the informal Hayne Beech Beds comprise soft, pale-weathering, siliceous radiolarian laminated shaly mudstones (cherts of literature) with some impure argillaceous limestones. Above, the Kersdown Chert Member comprises laminated cherts with interbedded shaly mudstones and a few limestones. The upper unit, the informal Bailey's Beds, consists of black shaly mudstones with limestones and minor cherts, the top 4m yields abundant spirally striated goniatites and pectinoid bivalves (Posidonia Beds).
Definition of Lower Boundary: Between Brushford and Ashbrittle the lower boundary is taken at the incoming of thin- to medium-bedded soft siliceous mudstones with impure limestones and cherts of the Bampton Limestone Formation above the hard black finely laminated unfossiliferous cherty mudstones of the underlying Doddiscombe Formation.
Definition of Upper Boundary: Between Brushford and Ashbrittle the upper boundary is taken at the incoming of dark grey predominantly unfossiliferous finely laminated silty mudstones with scattered siltstones of the overlying Dowhills Mudstone Formation above the highest limestone bed of the Bampton Limestone Formation.
Thickness: c.80m
Geographical Limits: Between Brushford (SS 92 26) and Ashbrittle (ST 04 21), Somerset.
Parent Unit: Teign Valley Group (TEVY)
Previous Name(s): Bampton Limestone Group (-2633)
Chert Formation (CTF)
Bampton Member (-4488)
Lower Culm Measures (-77)
Basement Formation (-1381)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Northwest face of Kiln Cottage Quarry, Bampton, northwest Devon. 23m of mudstone and limestone from the uppermost part of the Bampton Limestone Formation. Overlain by 5-6m exposure of dark grey mudstone and thin siltstone of the basal part of the Dowhills Mudstone Formation. 
Partial Type Section  Kersdown Quarry, Bampton, Devon. The disused quarry exposes all but the lowermost and topmost beds of the formation, all three divisions being seen. 40m of uniform, thin bedded siliceous mudstone interbedded with a few thin silicified limestone beds occupies the core of a tight anticline. These are overlain by 7m of cherts with interbedded mudstone and limestone of the Kersdown Chert Member. The upper part of the quarry shows a gradation into overlying black, faintly laminated siliceous mudstone at the base and alternations of limestone and mudstone above, up to 15m thick. 
Reference(s):
Swarbrick, E E. 1962. Facies changes in the Chert Formation of the Lower Culm Series of the Bampton area, north Devon. Proceedings of the Ussher Society, Vol 1, 30-31. 
Whiteley, M J. 2004. Culm Trough. 477-504 in British Lower Carboniferous Stratigraphy. Cossey, P J, Adams,A E, Purnell, M A, Whiteley, M J, Whyte, M A and Wright, V P (editors). Geological Conservation Review Series, No 29. (Peterborough: Joint Nature Conservation Committee). 
Webby, B D. and Thomas, J M. 1965. Whitsun field meeting: Devonian of west Somerset and the Carboniferous of north-east Devon. Proceedings of the Geologists Association, Vol. 76, 179-194. 
Ussher, W A E. 1900. The Devonian, Carboniferous and New Red Rocks of west Somerset, Devon and Cornwall. Proceedings of the Somerset Archeological and Natural History Society, Vol.46, 1-64. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable