The BGS Lexicon of Named Rock Units — Result Details

Pilton Mudstone Formation

Computer Code: PLT Preferred Map Code: notEntered
Status Code: Full
Age range: Famennian Age (DA) — Tournaisian Stage (CT)
Lithological Description: Grey mudstones and siltstones with thin- to thick-bedded, locally calcareous sandstones and beds and lenses of limestone. Sandstones are thickest and predominate in the lower half of the formation, whereas mudstones predominate in the upper half. Rich shelly neritic fauna occurs in the mudstones and limestones.
Definition of Lower Boundary: At the coast, the lower boundary is taken at the incoming of interbedded mudstones, siltstones and sandstones of the Pilton Mudstone Formation above a prominent slumped unit overlain by cross-bedded, medium-grained sandstones of the underlying Baggy Sandstone Formation. Inland, the boundary is taken above the highest, sugary, buff-brown, fine- to medium-grained feldspathic and micaceous sandstone, typical of the Baggy Sandstone Formation.
Definition of Upper Boundary: Between Brushford and Wellington the upper boundary is taken at the incoming of hard black finely laminated rarely fossiliferous cherty mudstones of the Doddiscombe Formation above the soft medium to dark grey mudstones with scattered very thin fossiliferous limestones, siltstones and sandstones of the underlying Pilton Mudstone Formation. West of South Molton, the upper boundary is taken at the gradational incoming of dark grey to black rarely fossiliferous, slightly siliceous, finely laminated mudstones of the overlying Doddiscombe Formation (Unit D of the Pilton Beds of Prentice (1960), above the fossiliferous mudstones with thin sandstones and siltstones of the underlying Pilton Mudstone Formation. The Doddiscombe Formation has not been mapped by BGS west of South Molton, instead it has been included in the Pilton Mudstone Formation and/or the Coddon Hill Chert Formation; further work is needed.
Thickness: 500m
Geographical Limits: Between Croyde and Wellington, north Devon (SS 70 28).
Parent Unit: Exmoor Group (EXM)
Previous Name(s): Pilton Shales (-1121)
Basement Beds (-3812)
Pilton Shales Group [Obsolete Name And Code: Use PLT] (PNSH)
Pilton Shales Formation (-1760)
Upper Pilton Beds [Obsolete Name And Code: See PLT] (UPN)
Pilton Beds (-456)
Lower Pilton Beds [Obsolete Name And Code: See PLT] (LPN)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Basal beds of the Pilton Mudstone and the underlying Baggy Sandstone are found 500m southsoutheast of Baggy House in the Croyde Bay area (Edmonds et al. 1979). 
Type Area  Outskirts of Braunton from near Buckland Cross to Chapel Hill (Edmonds et al. 1979). 
Partial Type Section  Coastal cliff from south side of Baggy Point to south side of Saunton Down, Croyde, north Devon. The section exposes the basal junction with the Baggy Sandstones Formation and the lower third of the Pilton Mudstone Formation. The sequence is folded. Edmonds et al. (1979). 
Reference(s):
Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
Hall, TM. 1867. On the relative distribution of fossils throughout the North Devon Series. Quarterly Journal of the Geological Society, London. Vol.23, 371-380. 
Edmonds, E A, Williams, B J and Taylor, R T. 1979. Geology of Bideford and Lundy Island. Memoir of the Geological Survey of Great Britain, Sheets 292 with 275, 276, 291, and part of 308 (England and Wales). 
Edmonds, E A, Whittaker, A, and Williams, B J. 1985. Geology of the country around Ilfracombe and Barnstaple. Memoir of the British Geological Survey, Sheets 277 and 293 (England and Wales). 
Prentice, J E. 1960. The Dinantian, Namurian and Lower Westphalian rocks of the region of southwest of Barnstaple, north Devon. Quarterly Journal of the Geological Society, London, Vol.115, 261-290. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E310 E293 E292 E311