The BGS Lexicon of Named Rock Units — Result Details
Bampton Limestone Formation
| Computer Code: | BPLM | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Visean Age (CV) — Visean Age (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 4 m 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. 80 m | ||
| Geographical Limits: | Between Brushford [SS 92 26] and Ashbrittle [ST 04 21], Somerset. | ||
| Parent Unit: | Teign Valley Group (TEVY) | ||
| Previous Name(s): | Bampton Limestones Group [Obsolete Name and Code: Use BPLM]
(-2009)
Bampton Limestone Group [Obsolete Name and Code: Use BPLM] (-2633) Lower Culm Group [Obsolete Name And Code: See TEVY and BPLM] (LCU) Bampton Member [Obsolete Name and Code: Use BPLM] (-4488) Lower Culm Measures (-77) Basement Formation [Obsolete Name and Code: Use BPLM] (-1381) Chert Formation (CTF) Upper Bampton Limestones [Obsolete Name and Code: Use BLEY, BPLM] (-3225) Lower Bampton Limestones [Obsolete Name and Code: Use HYBC, BPLM] (-3865) Middle Bampton Cherts [Obsolete Name and Code: Use KSDC, BPLM] (-3866) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Northwest face of Kiln Cottage Quarry, Bampton, northwest Devon. 23 m of mudstone and limestone from the uppermost part of the Bampton Limestone Formation. Overlain by 5-6 m 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. 40 m 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 7 m 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 15 m thick. | ||
| Type Area | Bampton, Devon. | ||
| 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. | |||
| Prentice, J E, 1967. Lower Carboniferous trilobites of north Devon and related species from Northern England. Bulletin of the British Museum, Vol.14, p.238. | |||
| 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. | |||
| 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. | |||
| 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). | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E310 E294 | |||