The BGS Lexicon of Named Rock Units — Result Details

Clynekirkton Sandstone Formation

Computer Code: CYK Preferred Map Code: Cyk
Status Code: Full
Age range: Callovian Age (JC) — Kimmeridgian Age (JD)
Lithological Description: Sandstone, variably cemented, sandy siltstone and sand. Some carbonaceous or calcareous beds and minor amounts of sandy limestone. Lower part has a rich marine shelly fauna. At Brora the overall thickness is at least 500 m. The lowermost Fascally Siltstone Member comprises 33.5 m of coarse siltstone, passing upwards into silty, fine-grained sandstone. It is overlain by 6.5 m of intensely bioturbated fine-grained muddy sandstone in several fining-upward cycles, rich in ammonites and bivalves, the Fascally Sandstone Member, that culminate in a massive sandy siltstone. Above are about 20 m of friable, fine-grained yellow sand with occasional carbonaceous debris, forming the Clynelish Quarry Sandstone Member, in which cemented sandstone with horizons of nodular silicified sandstone, flame structures and a rich fauna of ammonites and bivalves are locally seen. The overlying Brora Sandstone Member is at least 30 m of fine-grained friable sandstone with trough cross bedding and some lenticular quartz conglomerates. This is overlain by the Ardassie Limestone Member comprising at least 12 m of interbedded muddy carbonaceous sandstone and sandy limestone beds 0.3 to 1.1 m thick. Younger strata are present in boreholes to the north of Brora, and comprise about 400 m of pale grey, calcareous and silica-cemented sandstones with rare pebbles and subordinate shelly siltstones and mudstones or carbonaceous beds (Lee, 1925). These beds are not well known at outcrop and have been assigned to the Clynekirkton Sandstone Formation by BGS (1998), but there was no formal description given, nor type/reference sections proposed. The formation yields marine biota and microfossils throughout the beds up to the top of the Ardassie Limestone. The macrofauna is dominated by ammonites and bivalves; dinoflagellate cysts are abundant in the Fascally Sandstone Member (Riding, 2005). The beds overlying the Ardassie Limestone are of inferred mid and late Oxfordian (possibly earliest Kimmeridgian) age. The sequence stratigraphy of this formation was interpreted by Stephen and Davies (1998).
Definition of Lower Boundary: The lower boundary is defined by a change up from the bituminous sandy siltstone with mudstone intercalations of the Brora Brick Clay Member of the Strathsteven Mudstone Formation to the coarse siltstone to silty fine-grained sandstone of the Fascally Siltstone Member. The boundary is conformable.
Definition of Upper Boundary: Change up (not exposed) from sandstone to matrix-supported conglomerate of cobbles and boulders of sandstone, interbedded with laminated siltstone and sandstone (Kintradwell Boulder Beds Member of the Helmsdale Boulder Beds Formation, and Allt Na Cuile Sandstone [Formation])(Wright and Cox, 2001, fig.5.2).
Thickness: At the composite type section at Brora, the aggregated thickness of the exposed, lower part of the formation is at least 102 m, with an estimated additional 400 m of unexposed strata above.
Geographical Limits: The Clynekirkton Sandstone Formation is confined to the onshore area around Brora, on the Moray Firth, north-east Scotland. It is exposed on the foreshore around the River Brora estuary and in the cliffs bordering the River Brora. Its outcrop extends inland up to the Brora-Helmsdale Fault. It correlates offshore in the Inner Moray Firth with the upper part of the Beatrice Formation of the Fladen Group, plus at least part of the Heather Formation of the Humber Group (Richards et al., 1993).
Parent Unit: Sutherland Group (SUTH)
Previous Name(s): Brora Arenaceous Formation (BRARE)
Brora Arenaceous Series (-5001)
Brora Argillaceous Formation (Upper Part, Fascally Siltstone Member) (-5002)
Brora Argillaceous Series (Upper Part) (-5003)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Brora area, Sutherland, Scotland. 
Type Section  The type section of the Clynekirkton Sandstone Formation is a composite one in the foreshore south of Brora and in cliff sections on the south bank of the River Brora. The foreshore [NC 909 031] south of the River Brora estuary includes the type section of the Fascally Siltstone Member (Sykes, 1975). The type section of the Fascally Sandstone Member is on the north bank of the River Brora [NC 899 040]. The Clynelish Quarry Sandstone Member was named after Clynelish Quarry [NC 893 045], however the stratotype is in cliffs on the south bank of the River Brora: the lower part is 800 m WSW of the A9 road bridge [NC 898 038] and the upper part is 250 m downstream opposite the disused Brora colliery [NC 899 039] (Trewin and Hurst, 1993, localities 4 and 5 with amendments). The type section of the Brora Sandstone Member is composite. The majority of the section is in the cliffs on the south bank of the River Brora [NC 905 039], with the uppermost beds exposed south of Ardassie Point. The base of the section is 540 m west of the A9 road bridge, running eastwards to the fault, 140 m east of the bridge. From the fault, there is a gap in the exposure until the uppermost beds are seen on the foreshore south of Ardassie Point [NC 911 038 to 913 041] overlain here by the Ardassie Limestone Member at its type section. There is no type section for the Clynkirkton Sandstone Member but it was reported exposed near Clynekirkton church [NC 8940 0616] by Lee (1925, pp.96, 99)(Cox and Sumbler, 2002; Trewin and Hurst, 1993). 
Reference(s):
Wright, J K, and Cox, B M. 2001. British Upper Jurassic Stratigraphy (Oxfordian to Kimmeridgian). Geological Conservation Review Series. No. 21. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
Trewin, N H, and Hurst, A R (editors). 1993. Excursion guide to the geology of east Sutherland and Caithness. (Edinburgh: Scottish Academic Press.) 
Riding, J B. 2005. Middle and Upper Jurassic (Callovian to Kimmeridgian) palynology of the onshore Moray Firth Basin, northeast Scotland. Palynology, Vol. 29, 87-142. 
Stephen, K J, and Davies, R J. 1998. Documentation of Jurassic sedimentary cycles from the Moray Firth Basin, United Kingdom North Sea. 481-506 in Mesozoic and Cenozoic Sequence Stratigraphy of European Basins. SEPM Special Publication 60. Graciansky, P-C, Hardenbol, J, Jacquin, T, and Vail, P R (editors). 
Barron, A J M, Lott, G K, and Riding, J B. 2012. Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report RR/11/06. 
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. 
Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.). Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
British Geological Survey. 2002. Golspie. Scotland Sheet 103W. Solid and Drift. 1:50 000 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
British Geological Survey, 1998. Helmsdale. Scotland Sheet 103E. Solid and Drift. 1:50 000 Geology Series. British Geological Survey, Keyworth, Nottingham. 
Lee, G.W., 1925. Mesozoic rocks of East Sutherland and Ross, In: Read, H.H., Ross, G., Phemister, J. (Eds.), The geology of the country around Golspie, Sutherlandshire. Memoir of the Geological Survey, pp. 65-114. 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Lee, G W and Pringle, J. 1932. A synopsis of the Mesozoic rocks of Scotland. Transactions of the Geological Society of Glasgow, Vol.19, 158-224. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S103 S103