The BGS Lexicon of Named Rock Units — Result Details

Valtos Sandstone Formation

Computer Code: VTS Preferred Map Code: VtS
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: The formation is dominated by sandstone, medium- to coarse-grained, white to pale yellow, friable, cross-bedded in sets up to about 6m thick with prominent large (up to 1m in diameter), ovoid to near-spherical calcareous concretions or doggers produced following burial. Some of the medium-grained sandstones are significantly carbonaceous. The sandstone units are normally upward coarsening and capped by thin shelly limestones, normally coarse, sandy Neomiodon biosparites. Bioturbated green silty fissile mudstones and Neomiodon limestones occur within the sandstone units.
Definition of Lower Boundary: The base of the formation in the type area is marked by the first upsection occurrence of silty fissile mudstones with monotypic Neomiodon beds. These beds overlie the fissile mudstones of the Lealt Shale Formation; hence this boundary is gradational.
Definition of Upper Boundary: The top of the formation is defined by the first upsection occurrence of the oyster Praeexogyra hebridica (Forbes) in the lowermost beds of the Duntulm Formation. Lithologically, this boundary is gradational with the fissile mudstones with freshwater faunas of the uppermost Valtos Sandstone Formation being overlain by fissile mudstones with marine fossils of the lowermost Duntulm Formation. The formation is unconformably overlain by extrusive rocks of the Paleocene Skye Lava Group in places.
Thickness: Thicknesses from Harris and Hudson (1980) except where indicated. A maximum onshore thickness of 120m is estimated in Trotternish, Skye. Southwards, the formation thins significantly to about 70m in north-west Skye (British Geological Survey, 2006a), up to 52m on Raasay (British Geological Survey, 2006b), around 21m in Strathaird, Skye and about 60m on Eigg. At least 15m are present on Muck.
Geographical Limits: Hebrides Basin (Inner Hebrides and the Sea of the Hebrides sub-basins/troughs), northwest Scotland: onshore outcrops on Skye (Strathaird, Duirinish, Waternish and Trotternish districts), 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): Concretionary Sandstone Series (-1256)
Concretionary Sandstones (-2520)
Cyrena Limestones (-2521)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Foreshore exposures at Camas Sgiotaig, northwest Eigg. About 60m of strata dominated by sandstone but with minor mudstone, siltstone and limestone interbeds. Base on the Lealt Shale Formation is seen in the north; the top beneath the Duntulm Formation is present but not exposed. Hudson and Harris (1979, fig.7); Emeleus, 1997; Cox et al., 2002. 
Type Section  Cliffs between Valtos and Mealt Falls, Trotternish, northern Skye. About 95m seen from lower boundary on Lealt Shale Formation through to capping of dolerite sill. Strata dominated by sandstone but with a median unit including mudstone and limestone beds. The formation's stratigraphical top is well exposed about 2km to the northnorthwest. Harris and Hudson (1980); Cox et al., 2002; Morton and Hudson, 1995. 
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. 
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). 
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. 
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. 
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. 
Hudson, J D. 1964. The petrology of the sandstones of the Great Estuarine Series and the Jurassic palaeogeography of Scotland. Proceedings of the Geologists' Association, Vol.75, 499-528. 
Lee, G W. 1920. The Mesozoic rocks of Applecross, Raasay and North-east Skye. Memoir (District) of the Geological Survey of Great Britain (Scotland). (Edinburgh: His Majesty's Stationery Office.) 93pp. 
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. 
British Geological Survey. 2006a. Dunvegan. Scotland Sheet 80W. Bedrock and Superficial Deposits. 1:50 000 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
British Geological Survey. 2006. Raasay. Scotland Sheet 81W. Bedrock and Superficial Deposits. 1:50 000 Geology Series. (Keyworth, Nottingham: 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. 
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 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. 
Peach, B N, Horne, J, Woodward, H B, Clough, C T, Harker, A and Wedd, C B. 1910. The geology of Glenelg, Lochalsh and the south-east part of Skye (Explanation of One-Inch Map 71). Memoir (Sheet) of the Geological Survey of Great Britain (Scotland). (Edinburgh: His Majesty's Stationery Office.) 206pp. 
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 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S060 S071 S080 S080 S081 S090