The BGS Lexicon of Named Rock Units — Result Details

Staffin Bay Formation

Computer Code: STBA Preferred Map Code: StBa
Status Code: Full
Age range: Callovian Age (JC) — Callovian Age (JC)
Lithological Description: The Staffin Bay Formation is a succession of marine fissile mudstone and sandstone. A coarsening-upward trend is discernible from the dark grey, fissile mudstone with a shelly limestone bed, minor shell beds and laminated and rippled sandstones (the Upper Ostrea Member) being overlain by fine- to medium-grained bioturbated, carbonaceous sandstones with siltstones (the Belemnite Sands Member).
Definition of Lower Boundary: The base of the Formation in Trotternish is sharply-defined by the range base of dark-grey fissile mudstones with shell beds of the Upper Ostrea Member, which abruptly overlie the mottled green-grey-red clays of the Skudiburgh Formation. In Strathaird the base of the Staffin Bay Formation is also abrupt where the medium- to coarse-grained Carn Mor Sandstone Member sharply overlies the Skudiburgh Formation with a well-developed erosion surface.
Definition of Upper Boundary: The top of the formation in Trotternish is abruptly-defined; marked by a sharp facies change from the fine- to medium-grained sandstone of the Belemnite Sands Member to the bituminous fissile mudstones with thin glauconitic silts of the overlying Dunans Shale Member of the Staffin Shale Formation. In Strathaird, the uppermost surface of the Staffin Bay Formation is sharp, with a marked facies change from the medium- to coarse-grained sandstone of the Carn Mor Sandstone Member to the overlying silty clays of the Tobar Ceann Siltstone Member of the Staffin Shale Formation (Sykes, 1975, fig.6). The formation is unconformably overlain by extrusive rocks of the Paleocene Skye Lava Group in places.
Thickness: At the type section at Staffin Bay [NG 473 708], the formation is 15.95m thick and attains 19m in the wider Trotternish district (Hudson and Harris, 1979). The unit is significantly thinner to the south on Strathaird, where it is 9m (Sykes, 1975, p.68).
Geographical Limits: Hebrides Basin (Inner Hebrides and the Sea of the Hebrides sub-basins/troughs), northwest Scotland: onshore outcrops on Skye (Strathaird and Trotternish districts); not present on Raasay or Muck and not recorded on Eigg. Outcrops are separated/interrupted by Palaeogene igneous intrusions. The offshore extension of the formation within the sub-basins is uncertain (Fyfe et al., 1993).
Parent Unit: Not Applicable (-)
Previous Name(s): Upper "Ostrea" Beds And Belemnite Sands (-2451)
Staffin Bay Beds (-4346)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Coastal outcrop (foreshore) at Dunans. This is "Point 5" of Anderson and Dunham (1966, fig.10) and Morton and Hudson (1995, fig.38). The formation is fully exposed, 15.95m thick. Morton and Hudson, 1995, p. 272. 
Reference Section  Foreshore south of Rudha na h'Airigh Baine exposes 9m of fossiliferous, bioturbated, medium-grained sandstone (Carn Mor Sandstone Member). Sykes, 1975, p.68. 
Reference(s):
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. 
Anderson, F W and Cox, L R. 1948. The "Loch Staffin Beds" of Skye; with notes on the molluscan fauna of the Great Estuarine Series. Proceedings of the Royal Physical Society of Edinburgh, Vol.23, 103-122. 
Hudson, J D. 1963a. The recognition of salinity-controlled mollusc assemblages in the Great Estuarine Series (Middle Jurassic) of the Inner Hebrides. Palaeontology, Vol.6, 318-326. 
Hudson, J D. 1963b. The ecology and stratigraphical distribution of the invertebrate fauna of the Great Estuarine Series. Palaeontology, Vol.6, 327-348. 
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. 
Riding, J B. 1992. On the age of the Upper Ostrea Member, Staffin Bay Formation (Middle Jurassic) of north-west Skye. Scottish Journal of Geology, Vol.28, 155-158. 
Sykes, R M. 1975. The stratigraphy of the Callovian and Oxfordian stages (Middle-Upper Jurassic) in northern Scotland. Scottish Journal of Geology, Vol.11, 51-78. 
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. 
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 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. 
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.) 
Hudson, J D and Morton, N. 1969. Guide for Western Scotland. International Field Symposium on the British Jurassic, Excursion Number 4. University of Keele, Keele, U.K., 47pp. 
Riding, J B and Thomas, J E. 1997. Marine palynomorphs from the Staffin Bay and Staffin Shale formations (Middle-Upper Jurassic) of the Trotternish Peninsula, NW Skye. Scottish Journal of Geology, Vol.33, 59-74. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S071 S080 S090