The BGS Lexicon of Named Rock Units — Result Details

Bedruthan Formation

Computer Code: BEDN Preferred Map Code: notEntered
Status Code: Full
Age range: Emsian Age (DE) — Eifelian Age (DI)
Lithological Description: Grey-buff, fine-grained sandstone interlaminated with siltstone and grey-green mudstone. Sandstone proportion decreases upwards through the formation; subordinate dark grey units of mudstone and siltstone occur at several stratigraphical levels within the formation, with rare interbedded parallel-laminated sandstones. Elsewhere, sedimentary structures in sandstones include normal grading, bioturbation, cross-lamination, wispy bedding and load structures, all of which are lost when tight folding causes the amalgamation of sandstone units.
Definition of Lower Boundary: The lower boundary of the Bedruthan Formation is consistently a faulted contact with the Staddon Grit Formation. In the field, the lower boundary of the Bedruthan Formation would be identified by an abrupt change from fine- to-medium- grained grey to buff sandstone beds with interbedded laminated siltstone to grey-buff fine grained sandstones with siltstone of the Bedruthan Formation (as described in lithology section).
Definition of Upper Boundary: The upper boundary of the Bedruthan Formation is marked by a conformable junction with the overlying Trevose Slate Formation in the cliffs to the south of Lower Butter Cove, at [SW 8487 6993], near Queen Bess Rock. The transition in the field would be noted by a change from the grey-buff fine-grained sandstones with siltstone at the top of the Bedruthan Formation to the dark grey homogeneous mudstones with well-spaced pale grey laminae and sporadic lenticular bands of black slate of the lower Trevose Slate Formation.
Thickness: Up to 350 m.
Geographical Limits: A band of exposure trending east from coastal exposure around Bedruthan Steps [SW 8490 6950], through Burlawn [SW 9950 7010], then ESE through Bodmin.
Parent Unit: Not Applicable (-)
Previous Name(s): Bedruthan Slates (BEDSL)
Trevose Slate [Obsolete Name and Code: Use BEDN, SAH] (-1159)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Between a faulted contact at Carnewas Point and a conformable junction with the overlying Trevose Slate at an unnamed point north of Queen Bess Rock. Selwood and others, 1998. 
Reference(s):
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). 
Kirchgasser, W T, 1970. Conodonts from near the middle/upper Devonian boundary in north Cornwall. Palaeontology, Vol.13, 335-354. 
Reid, C, Barrow, G and Dewey, H. 1910. The geology of the country around Padstow and Camelford. Explanation of sheets 335 and 336. Memoir of the British Geological Survey, England and Wales. 
Ripley M J, 1964. The geology of the coastal area in the vicinity of Newquay, Cornwall. Unpublished PhD thesis, University of Birmingham. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable