| 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 [Obsolete Name and Code: Use SKU]
(-3680)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| 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). |
| 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). |
| Reference(s): |
| 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. |
| 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. |
| 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.) |
| 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. |
| 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. |
| 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. |
| 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). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S071
S080
S080
S090
|
