The BGS Lexicon of Named Rock Units — Result Details

Combe Mudstone Formation

Computer Code: CMMU Preferred Map Code: notEntered
Status Code: Full
Age range: Tournaisian Stage (CT) — Visean Stage (CV)
Lithological Description: Very fissile bluish black "shales", locally characterized by white, silty laminations and closely spaced vertical joints, particularly in higher horizons. Siliceous nodules become common in the upper part. The formation is unfossiliferous apart from ?wood fragments.
Definition of Lower Boundary: The lower boundary is taken at the incoming of bluish black and black mudstones of the Combe Mudstone Formation above the olive green and pale grey mudstones of the underlying Trusham Mudstone Formation.
Definition of Upper Boundary: The upper boundary is taken at the incoming of interbedded cherts and siliceous mudstones of the overlying Teign Chert Formation above the bluish black and black mudstones of the Combe Mudstone Formation. The boundary is taken at the base of the first bedded chert.
Thickness: 45m in the Ilsington area, thickening northwards to 90-200m in the Teign valley area.
Geographical Limits: Teign Valley (SX 84 84) and Ilsington area (SX 78 76), east Dartmoor, south Devon.
Parent Unit: Teign Valley Group (TEVY)
Previous Name(s): Combe Shale Formation [Obsolete Name And Code: Use CMMU] (CMSH)
Combe Shale (-2103)
Combe Formation (-144)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Road (B3193) cutting northwest of Lower Ashton, Teign valley, south Devon. Exposes most of the Formation, which is intruded by two dolerite sills. 
Reference(s):
Chesher, J A, 1968. The succession and structure of the Middle Teign Valley. Proceedings of the Ussher Society, Vol.2, 15-17. 
Selwood, E B, Edwards, R A, Simpson, S, Chesher, J A, Hamblin, R J O, Henson, M R, Riddolls, B W and Waters, R A. 1984. Geology of the countryside around Newton Abbot. Memoir of the British Geological Survey, Sheet 339 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable