The BGS Lexicon of Named Rock Units — Result Details

Kilmaluag Formation

Computer Code: KML Preferred Map Code: Kml
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Succession of interbedded grey calcareous mudstone, fissile mudstone and argillaceous limestone, commonly nodular. This calcareous unit contrasts markedly with the dominantly siliciclastic character of the remainder of the Great Estuarine Group. Prominent desiccation cracks are common, and some of the calcareous beds are dolomitic. Thin beds of fine-grained sandstone are developed in Trotternish; this is the "clastic facies" of (Andrews, 1985). Within the Great Estuarine Group, the formation is defined by the range of ostracod-rich calcareous strata. The ostracods are dominated by Darwinula and Theriosynoecum. Other fossils present are bivalves (e.g. Neomiodon and Unio), branchiopods, charophytes, fish, gastropods (e.g. Viviparus), mammals, plant debris and reptile bones. The vertebrate faunas have been described by Waldman and Savage (1972) and Waldman and Evans (1994). Riding et al. (1991) recorded marine and non-marine palynomorphs from the Kilmaluag Formation from Trotternish. The marine microplankton is low in abundance and does not include dinoflagellate cysts. The foraminiferal test linings and prasinophytes were probably swept into the barred lagoons during storms.
Definition of Lower Boundary: The base of the formation is defined by the range top of Praeexogyra hebridica-beareinglimestone or mudstone of the Duntulm Formation, and the first upsection occurrence of ostracod-bearing calcareous mudstones and marls/fissile mudstones.
Definition of Upper Boundary: The top of the formation is gradational and is marked by the range top of ostracod-bearing calcareous mudstones and marls/fissile mudstones, and the range base of the red, grey and green mudstones of the Skudiburgh Formation. The formation is unconformably overlain by extrusive rocks of the Paleocene Skye Lava Group in places.
Thickness: Thicknesses are from Harris and Hudson (1980, figs 3, 8). They also claim Anderson and Dunham's (Anderson and Dunham, 1966) 90 to 100 ft (27 to 33m) estimate for Trotternish is incorrect, probably repeated elsewhere (British Geological Survey, 2006, 2007). In Trotternish and on Strathaird, the formation is about 25m thick, and might be up to 23m on Waternish. It thins significantly southwards to 6 and 12m on Eigg and Muck respectively.
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): Ostracod Limestones (-1627)
Alternative Name(s): none recorded or not applicable
Partial Type Section  The north shore at Glen Scaladal, Strathaird, southern Skye. Almost fully exposed, mildly metamorphosed and lacks sandstones, but displays desiccation cracks and dolomitized breccias. Harris and Hudson, 1980, fig.9; Cox et al., 2002, fig.6.21 
Partial Type Section  Kilmaluag Bay, Trotternish, northern Skye. About 20m of strata, including base seen. Affected by intrusions, including at the top. Harris and Hudson, 1980; Morton and Hudson, 1995, table 3. 
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. 
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. 
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 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). 
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. 
Waldman, M and Evans, S E. 1972. Lepidosauromorph reptiles from the Middle Jurassic of Skye. Zoological Journal of the Linnean Society of London, Vol.112, 135-150. 
British Geological Survey. 2006. Staffin. Scotland Sheet 90. Bedrock and Superficial Deposits. 1:50 000 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
Waldman, M and Savage, R J G. 1972. The first Jurassic mammal from Scotland. Journal of the Geological Society of London, Vol.128, 119-125. 
British Geological Survey. 2007. Portree. Scotland Sheet 80E. Bedrock and Superficial Deposits. 1:50 000 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S060 S071 S080 S080 S090