The BGS Lexicon of Named Rock Units — Result Details

Bearreraig Sandstone Formation

Computer Code: BEAS Preferred Map Code: BeaS
Status Code: Full
Age range: Toarcian Age (JT) — Bajocian Age (JB)
Lithological Description: The formation is dominated by fossiliferous calcareous sandstone with subordinate limestone and fissile mudstone. The successions present in various districts of Skye, on Raasay, Mull and Ardnamurchan and offshore differ significantly in thicknesses and lithologies (see SUPPLEMENTARY INFORMATION).
Definition of Lower Boundary: The lower boundary of the formation is a sharp, planar, apparently conformable lithological change from ferruginous limestone of the Raasay Ironstone Formation to the grey fissile mudstones of the Dun Caan Shales Member.
Definition of Upper Boundary: The blocky grey or brown fissile mudstone with ammonites of the Garantiana Mudstone Member passes gradationally into the black, bituminous, fissile mudstone of the Cullaidh Shale Formation. The base of the Cullaidh Shale Formation is taken at the first upsection occurrence of carbonaceous, fissile mudstones with fish scales. There are marked facies variations which make the boundary between the Garantiana Mudstone Member and the Cullaidh Shale Formation difficult to identify (Harris and Hudson, 1980, p.234, 235). The formation is unconformably overlain by extrusive rocks of the Paleocene Skye Lava Group in places.
Thickness: Thicknesses quoted by authors for the same localities may be at considerable variance, due to the nature of the topography (e.g. sea cliffs) and of much of the sequences (laterally variable shallow marine sandstone), and to the difficulties of aggregating thickness ranges given for components. All thicknesses below are from Morton (1965) except where indicated. In Trotternish, north Skye, including the type section, the formation ranges from 156 to 228m thick (see also Morton, 1976). On Strathaird [NG 52 11 to 56 21], it varies between 256 (Faoilean) and 488m (southern tip), and on Raasay attains up to about 214m. The succession at Glas Bheinn Beag [NG 585 257], near Dunan is approximately 235m. On Ardnamurchan, the formation is between 20m (British Geological Survey, 2009) and 37m (Richey and Thomas, 1930) thick. Strata attributed to the formation on southeast Mull total about 30m. Greater thicknesses might be present offshore (Fyfe et al., 1993).
Geographical Limits: Hebrides Basin (Inner Hebrides and the Sea of the Hebrides sub-basins/troughs), northwest Scotland: onshore outcrops on Ardnamurchan (Richey and Thomas, 1930), Mull, Eigg (Emeleus, 1997), Raasay, Skye (Dunan, Strathaird and Trotternish) (Morton, 1965). Outcrops are separated/interrupted by Palaeogene igneous intrusions. Some continuity of the formation offshore within the sub-basins is inferred but extent is uncertain (Fyfe et al., 1993).
Parent Unit: Not Applicable (-)
Previous Name(s): Inferior Oolite (-1341)
Bearreraig Sandstone Series (-2594)
Alternative Name(s): none recorded or not applicable
Type Section  Well-exposed coastal and cliff outcrops at Bearreraig Bay on the east coast of the Trotternish Peninsula, 10km north of Portree, northern Skye. All of the six members apart from the uppermost, Garantiana Mudstone, are exposed. Morton (1965; 1976; 1991); Morton and Hudson (1995); Cox, Page and Morton(2002). 
Morton, N and Hudson, J D, 1995. Field Guide to the Jurassic of the Isles of Raasay and Skye, Inner Hebrides, north-west Scotland. In: Taylor, P D (editor), Field Geology of the British Jurassic. Geological Society of London, 209-280. 
Morton, N. 1965. The Bearrenaig Sandstone Series (Middle Jurassic) of Skye and Raasay. Scottish Journal of Geology, Vol.1, 189-216. 
Cox, B M, Page, K N and Morton, N, 2002. The Middle Jurassic stratigraphy of Scotland. In Cox, B M and Sumbler, M G (editors), British Middle Jurassic Stratigraphy. Geological Conservation Review Series, Vol.26. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
Harris, J P and Hudson, J D. 1980. Lithostratigraphy of the Great Estuarine Group (Middle Jurassic), Inner Hebrides. Scottish Journal of Geology, Vol.16(2/3), 231-250. 
Morton, N. 1991. Proposal for selection of Bearreraig (Isle of Skye, N.W. Scotland) as GSSP for the base of the Bajocian Stage. 69-79 in Morton, N. (Ed.). Proceedings of a conference on Aalenian and Bajocian stratigraphy, Isle of Skye, Scotland, 13-20 April 1991. IUGS International Subcommission on Jurassic Stratigraphy. Aalenian and Bajocian working groups. Birkbeck College, University of London, London, September 1991. 
Riding, J B, Walton, W and Shaw, D. 1991. Toarcian to Bathonian (Jurassic) palynology of the Inner Hebrides, northwest Scotland. Palynology, Vol.15, 115-179. 
Smith, S M. 1960. Metamorphism of the Jurassic rocks of Glas Bheinn Bheag, near Dunan, Isle of Skye. Geological Magazine, Vol.97, 466-479. 
Emeleus, C H and Bell, B R. 2005. British Regional Geology: the Palaeogene volcanic districts of Scotland (Fourth Edition). (Nottingham: British Geological Survey.) x + 214pp. 
Parsons, C F. 1980. Aalenian and Bajocian correlation chart. 3-21 in Cope, J C W, Duff, K L, Parsons, C F, Torrens, H S, Wimbledon, W A and Wright, J K. A correlation of Jurassic rocks in the British Isles. Part Two: Middle and Upper Jurassic. Geological Society of London, Special Report, No.15. 
British Geological Survey. 2009. Ardnamurchan Central Complex. Bedrock and Superficial Deposits. 1:25 000 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
Morton, N. 1976. Bajocian (Jurassic) stratigraphy in Skye, Western Scotland. Scottish Journal of Geology, Vol.12, 23-33. 
Lee, G W and Pringle, J. 1932. A synopsis of the Mesozoic rocks of Scotland. Transactions of the Geological Society of Glasgow, Vol.19, 158-224. 
Morton, N and Hudson, J D. 1964. The stratigraphical nomenclature of the Lower and Middle Jurassic rocks of the Hebrides. Geological Magazine, Vol.101, 531-534. 
Richey, J E and Thomas, H H. 1930. The geology of Ardnamurchan, north-west Mull and Coll. Memoir of the Geological Survey of Great Britain. Sheet 51 and part of sheet 52 (Scotland). 
Fyfe, J A, Long, D and Evans, D, 1993. United Kingdom offshore regional report: the geology of the Malin - Hebrides sea area (London: HMSO for the British Geological Survey). 
Emeleus, C H. 1997. Geology of Rum and the adjacent islands. Memoir (sheet) of the Geological Survey of Great Britain (Scotland) (60). (The Stationery Office for the British Geological Survey.) 171pp. 
Anderson, F W and Dunham, K C. 1966. The geology of northern Skye. Memoirs of the Geological Survey of Great Britain, Scotland. Sheet 80 and parts of sheets 81, 90 and 91. Edinburgh, HMSO. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S044 S051 S060 S061 S071 S080 S081 S090