The BGS Lexicon of Named Rock Units — Result Details

Achrimsdale Sandstone Member

Computer Code: ACHSD Preferred Map Code: notEntered
Status Code: Full
Age range: Oxfordian Age (JO) — Kimmeridgian Age (JD)
Lithological Description: Sandstone, pale grey, calcareous and silica-cemented, bioturbated, with rare pebbles and subordinate mudstones and shelly siltstones. Mudstones may include resinous lignite and coaly beds and the siltstone beds locally contain scattered carbonaceous fragments and microcrystalline limestone nodules (Lee, 1925, p. 99; Trewin and Hurst, 1993, pp 91-94; British Geological Survey, 1998). Lee (1925, p. 99) reports the find of a cast of a crinoid stem. BGS field data (1891 and 1923) mentions "oolitic sand" seen in stream beds on the outcrop and worm tubes in carbonaceous sandy mudstone and muddy sandstone on the foreshore.
Definition of Lower Boundary: The lower boundary is defined by a change up from the interbedded muddy carbonaceous sandstone and sandy limestone beds of the Ardassie Limestone Member to the sandstone and mudstone of the Achrimsdale Sandstone Member. The nature of the boundary is unknown but is inferred to be 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: Estimated 400m.
Geographical Limits: The Achrimsdale Sandstone Member is confined to the onshore area north of Brora, on the Moray Firth, north-east Scotland. Its outcrop extends inland up to the Brora-Helmsdale Fault.
Parent Unit: Clynekirkton Sandstone Formation (CYK)
Previous Name(s): Clynekirkton Sandstone Member [Obsolete Name And Code: See ACHSD] (CYKSD)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Brora area, Sutherland, Scotland. 
Reference Section  Foreshore at Lothbeg [NC 946 095] exposes bioturbated sandstone and mudstone near the top of the member, although the top is not exposed (Trewin and Hurst, 1993, pp 91-94). 
Reference(s):
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. 
Barron, A J M, and Riding, J B. 2014. A revision of the Jurassic (Bathonian to Oxfordian) lithostratigraphy of the onshore Moray Firth Basin, north-east Scotland. Proceedings of the Geologists' Association, Vol. 125, pp. 74-82. 
Trewin, N H, and Hurst, A R (editors). 1993. Excursion guide to the geology of east Sutherland and Caithness. (Edinburgh: Scottish Academic Press.) 
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.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable