The BGS Lexicon of Named Rock Units — Result Details

Barras Nose Formation

Computer Code: BNF Preferred Map Code: BNF
Status Code: Full
Age range: Tournaisian Stage (CT) — Visean Stage (CV)
Lithological Description: Dark grey and black mudstones with variably abundant very thin beds and laminae of cross laminated and graded silstone and sandstone. The mudstones contain scattered sideritic, carbonaceous silty sandstone and argillaceous limestone nodules, containing goniatites. A thin fossiliferous limestone is present at or very near the top of the Formation. Volcanic material locally occurs as lenses of sheared vesicular lava and tuff.
Definition of Lower Boundary: The depositional lower boundary is not seen as the lower boundary is everywhere tectonic.
Definition of Upper Boundary: The upper boundary is taken at the sharp contact of tuffs, lavas and agglomerates of the overlying Tintagel Volcanic Formation with the mudstones and thin siltstones of the Barras Nose Formation.
Thickness: 21m+ on the coast in the Boscastle/Tintagel area; poorly constrained as a result of deformation.
Geographical Limits: Occurs between the Boscastle/Tintagel area (SX 07 89), north Cornwall and the Launceston area (SX 30 78), east Cornwall. The outcrop in east Cornwall (BGS, 1993) needs further investigation.
Parent Unit: Teign Valley Group (TEVY)
Previous Name(s): Lower Blue-Black Slates (-2003)
Barras Nose Beds (-3231)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  In the cove and at the side of the cliff-top path. McKeown, M C, et al, 1973. 
Partial Type Section  Coastal cliff, on the west side of Barras Nose, Tintagel, north Cornwall. The upper 12m of the Formation and the contact with the overlying Tintagel Volcanic Formation are exposed in the section; the faulted base of the Formation is also visible. Freshney et al. (1972). 
Reference(s):
Parkinson, J, 1903. On the geology of the Tintagel and Davidstow district, Quarterly Journal of the Geological Society,Vol.59,408-421. 
Dewey, H, 1909. On Overthrusts at Tintagel (North Cornwall). Quarterly Journal of the Geological Society, Vol.65, 265-280. 
Selwood, E B, Thomas, J M, Williams, B J, Clayton, R, Durning, B, Smith, O and Warr, L N, 1998. Geology of the country around Trevose Head and Camelford. Memoir of the British Geological Survey, sheets 335 and 336 (England and Wales). 
Freshney, E C, McKeown, M C and Williams, M. 1972. Geology of the coast between Tintagel and Bude. Memoir of the Geological Survey of Great Britain, part of sheet 322 (England and Wales). 
McKeown, M C, Edmonds, E A, Williams, M, Freshney, E C and Masson Smith, D J. 1973. Geology of the country around Boscastle and Holsworthy. Memoir of the British Geological Survey, sheets 322 and 323 (England and Wales). 
British Geological Survey, 1993. Tavistock. England and Wales Sheet 337. Solid and Drift 1:50 000 Provisional Series (Keyworth, Nottingham: British Geological Survey). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E322 E336 E337