The BGS Lexicon of Named Rock Units — Result Details

Creg Agneash Sandstone Formation

Computer Code: CGA Preferred Map Code: notEntered
Status Code: Full
Age range: Arenig Series (OR) — Arenig Series (OR)
Lithological Description: White quartz arenite, thin or medium bedded, but locally thick or very thick bedded. In the lower part sandstone is interbedded with laminated siltstone and mudstone, but this passes upwards into thin persistent interbeds of dark grey silty mudstone. The sandstone is massive to weakly graded and slump folding is widely developed. Deposition was from medium concentration turbidity currents (Woodcock et al., 1999). Further description is given by Chadwick et al. (2001, p. 24-25). A sparse, low-diversity acritarch flora is not diagnostic and the probable Arenig age is extrapolated from the overlying Maughold Mudstone and underlying Lonan Sandstone formations.
Definition of Lower Boundary: The base is transitional from the underlying Lonan Sandstone Formation with quartz arenite beds becoming increasingly abundant over an interval of several tens of metres within mudstone of Lonan Sandstone Formation type; the base of the Creg Agneash Formation is taken where quartz arenite becomes the dominant lithology.
Definition of Upper Boundary: Transitional into the overlying Maughold Formation; sandstone beds progressively decrease in number and top is taken at the abrupt change to laminated silty mudstone.
Thickness: At least 180 m and possibly up to 750 m though there may be some repetition by folding.
Geographical Limits: Eastern Isle of Man, south-west from Maughold Head, to inland from Douglas.
Parent Unit: Manx Group (MANX)
Previous Name(s): Agneash Grit (Manx Slates) [Obsolete Name and Code: Use CGA] (AGNG)
Maughold Banded Group [Obsolete Name and Code: Use MGD, CGA, CRMR, MHL] (-2687)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The type section is Maughold Head [SC 4986 9142], Isle of Man (Woodcock et al., 1999). 
Reference(s):
Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. 
Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) 
Millward, D, and Stone, P. 2012. Stratigraphical framework for the Ordovician and Silurian sedimentary strata of northern England and the Isle of Man. British Geological Survey Research Report, RR/12/04. 119pp. 
Woodcock N H, Morris J H, Quirk D G, Barnes R P, Burnett D, Fitches W R, Kennan P S and Power G M. 1999. Revised lithostratigraphy of the Manx Group, Isle of Man. 45-68 in 'In sight of the suture' the Palaeozoic geology of the Isle of Man in its lapetus Ocean context. Woodcock N H, Fitches W R, Quirk D G and Barnes R P [editors]. Geological Society of London, Special Publication No. 160. 
Simpson A. 1963. The stratigraphy and tectonics of the Manx Slate Series. Quarterly Journal of the Geological Society of London, Vol. 119, 367-400 
Lamplugh G W. 1903. The geology of the Isle of Man. Memoir Geological Survey of Great Britain. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E400