The BGS Lexicon of Named Rock Units — Result Details

Doddiscombe Formation

Computer Code: DDC Preferred Map Code: notEntered
Status Code: Full
Age range: Tournaisian Stage (CT) — Visean Stage (CV)
Lithological Description: Hard, black, slightly siliceous, finely laminated mudstones with sparse very thin siltstone beds. There are scattered thin lenticular ?chert and phosphate nodules and sparse impure limestones and local pale calcareous mudstones. The formation is rarely fossiliferous.
Definition of Lower Boundary: Between Brushford and Wellington the lower boundary is taken at the incoming of hard black finely laminated unfossiliferous, slightly siliceous mudstones of the Doddiscombe Formation above the soft medium to dark grey mudstones with scattered very thin limestones, siltstones and sandstones of the underlying Pilton Mudstone Formation. West of South Molton, the lower boundary is taken at the incoming of dark grey to black, rarely fossiliferous slightly siliceous, finely laminated mudstones (Unit D of the Pilton Beds of Prentice 1960), known to equate with the Doddiscombe Formation, 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 Codden Hill Chert Formation. Further work is therefore needed.
Definition of Upper Boundary: Between Brushford and Wellington the upper 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. West of South Molton, the upper boundary is taken at the incoming of dark grey interbedded siliceous mudstones and shaly mudstones of the overlying Coddon Hill Chert Formation above the dark unfossiliferous slightly siliceous mudstones (Unit D of the Pilton Beds of Prentice 1960), known to equate with the Doddiscombe Formation. Neither this boundary nor the Doddiscombe Formation has been mapped by BGS west of South Molton and further work is needed.
Thickness: 8 to 80m; lower thickness likely to be tectonic.
Geographical Limits: Between Brushford (SS 92 26) and Wellington (ST 13 20), Somerset. Known to extend west of South Molton to the Barnstaple area (SS 50 33) as the dark unfossilferous silty mudstones, Unit D of the Pilton Beds of Prentice (1960). This unit has not been mapped by BGS west of South Molton and further work is needed.
Parent Unit: Teign Valley Group (TEVY)
Previous Name(s): Basement Beds (-3812)
Basement Formation (Pars) (-4598)
Pilton Shales (Pars) (-4599)
Landkey Formation (-1494)
Doddiscombe Beds (-205)
Lower Culm Measures (Pars) (-3354)
Pilton Beds (Pars) (-2150)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Doddiscombe quarry, 3km northeast of Bampton, northeast Devon. 6.9m mudstone, pale to dark grey massive to planar laminated present. Upper and lower boundaries not exposed. 
Reference(s):
Ussher, W A E. 1887. The Culm of Devonshire. Geological Magazine, Vol.24, 10-17. 
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. 
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. 
Jackson, P C. 1991. The Dinantian stratigraphy of northwest Devon. Proceedings of the Yorkshire Geological Society, Vol.48, 447-460. 
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. 
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:
E310 E311