The BGS Lexicon of Named Rock Units — Result Details

Skudiburgh Formation

Computer Code: SKU Preferred Map Code: Sku
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Succession of mottled red and grey-green silty mudstone sporadically rich in small (2-10cm in diameter) calcareous septarian concretions. Green-weathering lenticular siltstones are common and thin, lenticular fining-upwards calcareous sandstones are developed in Trotternish. The sparse fossils are all freshwater, and comprise bivalves (e.g. Unio), gastropods (e.g. Viviparus), fish teeth and plant fragments.
Definition of Lower Boundary: The base is gradational and is defined by the base of mottled red and grey-green mudstones, and the range top of ostracod-bearing calcareous mudstones and fissile mudstones of the underlying Kilmaluag Formation.
Definition of Upper Boundary: The top of the formation is sharply-defined, and is marked by the change from mottled red and grey-green mudstones to dark, shelly fissile mudstones (Upper Ostrea Member, Staffin Bay Formation) in Trotternish and a non-sequence overlain by sandstone (Carn Mor Sandstone Member, Staffin Bay Formation) in Strathaird. The formation is unconformably overlain by extrusive rocks of the Paleocene Skye Lava Group in places.
Thickness: A composite of the two partial type sections gives a thickness of about 15 to 16m in Trotternish. Thicknesses quoted for Strathaird vary from 10 to 11m (Harris and Hudson, 1980; Harris, 1992) to 16 to 18m (Hudson, 1962; Hudson and Harris, 1979). The formation might be present in Waternish, but has not been recognized on Raasay, Eigg or Muck (Harris and Hudson, 1980, fig.3; Emeleus, 1997).
Geographical Limits: Hebrides Basin (Inner Hebrides and the Sea of the Hebrides sub-basins/troughs), northwest Scotland: onshore outcrops on Skye (Strathaird, Trotternish and possibly also Waternish districts); not recorded on Raasay, Eigg and Muck. Outcrops are separated/interrupted by Palaeogene igneous intrusions. The offshore extension of the parent Great Estuarine Group within the sub-basins is inferred but uncertain (Fyfe et al., 1993).
Parent Unit: Great Estuarine Group (GEST)
Previous Name(s): Mottled Clays (-3680)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Coastal outcrop at Skudiburgh, Trotternish, northern Skye, displaying about 4m of ripple-marked silty mudstone and cross-bedded sandstone. The base and top are not exposed. Harris and Hudson, 1980; Cox et al., 2002, figs 6.24 - 6.26. 
Partial Type Section  Foreshore at Digg, Staffin Bay, Trotternish, northern Skye, base not seen and affected by strike faulting. Anderson and Dunham, 1966; Harris and Hudson, 1980. 
Reference(s):
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). 
Hudson, J D. 1962. The stratigraphy of the Great Estuarine Series (Middle Jurassic) of the Inner Hebrides. Transactions of the Edinburgh Geological Society, Vol.19, 135-165. 
Anderson, F W. 1948. Algal beds in the Great Estuarine Series of Skye. Proceedings of the Royal Physical Society of Edinburgh, Vol.23, 123-141. 
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. 
Harris, J P. 1992. Mid-Jurassic lagoonal delta systems in the Hebridean basins: thickness and facies distribution patterns of potential reservoir sandbodies. 111-144 in Parnell, J (Ed.). Basins on the Atlantic Seaboard: Petroleum Geology, Sedimentology and Basin Evolution. Geological Society Special Publication, No.62. 
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. 
Andrews, J E. 1985. The sedimentary facies of a late Bathonian regressive episode: the Kilmaluag and Skidiburgh Formations of the Great Estuarine Group, Inner Hebrides, Scotland. Journal of the Geological Society of London, Vol.142, 1119-1137. 
Hudson, J D and Harris, J P. 1979. Sedimentology of the Great Estuarine Group (Middle Jurassic) of north-west Scotland. Symposium sur la Sedimentation de Jurassique Ouest Europeen, Paris, 9-10 May 1977, Association des Sedimentologists Francais, Publication Speciale, No.1, 1-13. 
Hudson, J D and Andrews, J E. 1987. The diagenesis of the Great Estuarine Group, Middle Jurasic, Inner Hebrides, Scotland. 259-276 in Marshall, J D (Ed.), Diagenesis of Sedimentary Sequences. Geological Society Special Publication, No.36. 
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. 
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.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S071 S080 S080 S090