The BGS Lexicon of Named Rock Units — Result Details

Trusham Mudstone Formation

Computer Code: TMMU Preferred Map Code: notEntered
Status Code: Full
Age range: Tournaisian Stage (CT) — Tournaisian Stage (CT)
Lithological Description: Olive green, soapy "shales" exhibiting a conchoidal fracture and pale grey "shales" with calcareous micaceous laminae. The small bivalve Sanguinolites? ellipticus is locally abundant in the upper part of the Formation. Sparse shelly benthos and pelagic ostracods are locally present.
Definition of Lower Boundary: The lower boundary is taken at the gradational incoming of pale grey and green micaceous shales of the Trusham Mudstone Formation above the dark blue-grey or bluish green-grey mottled shales and calcareous beds of the underlying Hyner Mudstone Formation. Commonly this boundary cannot be detected in the metamorphic aureole of the Dartmoor Granite.
Definition of Upper Boundary: The upper boundary is taken at the incoming of bluish black and black mudstones of the overlying Combe Mudstone Formation above the olive green and pale grey mudstones of the Trusham Mudstone Formation.
Thickness: 65m
Geographical Limits: Middle Teign Valley and Ilsington areas, eastern Dartmoor (SX 84 85), south Devon.
Parent Unit: Not Applicable (-)
Previous Name(s): Trusham Formation (-3728)
Trusham Shale (-2490)
Trusham Shale Formation [Obsolete Name And Code: Use TMMU] (TMSH)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Track section north of Leigh, near Trusham (SX855 822), Devon. Much of theFormation is exposed (64m), but neither upper nor lower contacts are seen. The section yields Early Tournaisian ostracods. Selwood et al., 1984. 
Reference(s):
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). 
Chesher, J A, 1968. The succession and structure of the Middle Teign Valley. Proceedings of the Ussher Society, Vol.2, 15-17. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable