The BGS Lexicon of Named Rock Units — Result Details

Bealsmill Formation

Computer Code: BEAL Preferred Map Code: notEntered
Status Code: Full
Age range: Namurian Stage (CN) — Namurian Stage (CN)
Lithological Description: Thin- to thick-bedded commonly coarse and feldspathic sandstones interbedded with siltstones and dark grey mudstones. Scattered beds of ill-sorted pebble to cobble conglomerate up to 2m thick contain clasts including chert, lava and limestone as well as derived Dinantian and ?Namurian fossils. Some channels are present.
Definition of Lower Boundary: The depositional lower boundary is not seen as the base is always faulted. The lower boundary is thought to post-date the D1 deformation phase, with the formation resting unconformably on Dinantian sequences.
Definition of Upper Boundary: The depositional upper boundary is not seen but probably tectonic.
Thickness: Unknown. Minimum thickness 120m
Geographical Limits: Mapped from Altarnun (SX 22 81), east Cornwall to northwest Dartmoor (SX 49 85), but thought to extend into the southwestern part of the Okehampton area (SX 53 87), mid Devon, where is has been mapped as Crackington Formation. Formational diagnosis needs further work, as does the area where it has not been mapped.
Parent Unit: Holsworthy Group (HOWY)
Previous Name(s): Eggesford-Type Culm [Obsolete Name and Code: Use BEAL, CKF] (-47)
Middle or Exeter-Type Culm [Obsolete Name and Code: Use CKF, BEAL] (-3835)
Okehampton Sandstone Group [Obsolete Name and Code: Use CKF, BEAL] (-3836)
Bealesmill Sandstone Formation [Obsolete Name and Code: Use BEAL] (-4451)
Bealsmill Sandstone Formation [Obsolete Name and Code: Use BEAL] (-4452)
Crackington Formation (CKF)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Bealsmill, Cornwall. 
Partial Type Section  Carthamartha Crags, south of Launceston, east Cornwall. Located about 700m eastnortheast of Rezare. Only a small part of the formation is exposed with no base or top. Turner (1982); Sellwood and Thomas (1986). 
Reference(s):
Ussher, W A E. 1892. The British Culm Measures. Proceedings of the Somerset Archeological and Natural History Society, Vol.38, 111-219. 
Turner, P J. 1982. Aspects of the evolution of the Hercynides in central southwest England. Unpublished PhD thesis, University of Exeter. 
Dearman W R and Butcher, N E. 1959. The geology of the Devonian and Carboniferous rocks of the northwest border of the Dartmoor Granite, Devonshire. Proceedings of the Geologists' Association, Vol.70, 51-92. 
Edmonds, E A, Wright, J E, Beer, K E, Hawkes, J R, Fenning, P J, Freshney, E C, Lovelock, P E R, McKeown, M C, Ramsbottom, W H C and Williams, M. 1968. Geology of the country around Okehampton. Memoir of the Geological Survey of Great Britain, Sheet 324 (England and Wales). 
Isaac, K P. 1985. Thrust and nappe tectonics of west Devon. Proceedings of the Geologists' Association, Vol.96, 109-127. 
Ussher, W A E. 1887. The Culm of Devonshire. Geological Magazine, Vol.24, 10-17. 
Sellwood, E B and Thomas, J M. 1986. Variscan facies and structure in central southwest England. Journal of the Geological Society, London, Vol.153, 199-207. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable