The BGS Lexicon of Named Rock Units — Result Details

Ardvreck Group

Computer Code: ARDV Preferred Map Code: notEntered
Status Code: Full
Age range: Comley Series (EC) — Comley Series (EC)
Lithological Description: The lowest unit of the group is the Basal Quartzite Member (Eriboll Formation), which is cross-bedded, fine- to medium-grained, quartz arenite, although locally the base reaches pebble grade. Compositionally, the basal part is also feldspar rich, up to subarkose in places, but the proportion and grain size decreases rapidly upwards. The unit is overlain by cross-bedded quartz arenites of the Pipe Rock Member (Eriboll Formation), which is a fine- to coarse-grained, quartz arenite with abundant Skolithos burrows at most levels. Localised staining by ferric iron oxide is present in the upper part of the Member, commonly differentially distributed between burrows and matrix. The Eriboll Formation is conformably overlain by dolomitic siltstones, with minor dolomitic grainstones and dolomitic sandstones, of the Fucoid Beds Member (An t-Sron Formation). The Fucoid Beds Member is in turn overlain by the Salterella Grit Member (An t-Sron Formation) which marks a return to cross-bedded quartz arenites containing Skolithos, but also containing abundant agglutinated shells of Salterella.
Definition of Lower Boundary: The lower boundary is placed where white or pale grey, granule- or pebble-grade quartz arenites/subarkoses of the Basal Quartzite Member (Eriboll Formation) rest unconformably on rocks of the Lewisian Complex or the Torridon Group.
Definition of Upper Boundary: The upper boundary is placed where dolostones of the Ghrudaidh Formation (Durness Group), which may be locally sandy or muddy, lie conformably on the Salterella Grit Member (An t-Sron Formation) of the Ardvreck Group.
Thickness: 93-142m
Geographical Limits: The Ardvreck Group forms a narrow belt, extending along the northwestern side of Scotland from the Durness-Eriboll area, through Assynt, Dundonnell, Kinlochewe and Kishorn, to Skye.
Parent Unit: Not Applicable (-)
Previous Name(s): Eriboll Group (-1952)
Alternative Name(s): none recorded or not applicable
Type Area  Road cuttings along the A837 to the west and east of Skiag Bridge Road junction, on the north side of Loch Assynt (Sutherland). Together with additional natural outcrops to the north of the road as far north as NC 2600. Peach et al. 1907. 
Reference Section  Coastline of An t-Sron and the hillside above Kempie, on the east side of Loch Eriboll, Sutherland. Peach et al. 1907. 
Peach, B N, Home, J, Gunn, W, Clough, C T and Hinxman, L W, 1907. The Geological Structure of the northwest Highlands of Scotland. Memoir of the Geological Survey of Great Britain. 
Wright, D T and Knight, I. 1995. A revised chronostratigraphy for the lower Durness Group. Scottish Journal of Geology, Vol. 31, 11-22. 
Krabbendam, M, Goodenough, K M, Parsons, I, Leslie, A G, Smith, P, Key, R, Loughlin, S C, and Pickett, E A (in prep). Classical areas of British Geology: Assynt. British Geological Survey. 
Johnston, G S and Mykura, W. 1989. British regional geology: the Northern Highlands (4th edition) (London: HMSO for the British Geological Survey.) 
Mckie, T. 1989. Barrier-island to tidal shelf transition in the Early Cambrian Eriboll Sandstone. Scottish Journal of Geology, 25, 273-293. 
Prigmore, J K and Rushton, A W A. 1999. Scotland: Cambrian and Ordovician of the Hebridean Terrane. 295-315 in British Cambrian to Ordovician Stratigraphy. Rushton, A W A, Owen, A W, Owens, R M and Prigmore, J K (editors). Geological Conservation Review Series. (Joint Nature Conservation Committee.) 
Mckie, T. 1990. Tidal and storm influenced sedimentation from a Cambrian transgressive passive margin sequence. Journal of the Geological Society, London, 147, 785-794. 
Mckie, T. 1990. A model for marine shelf storm deposition in the Lower Cambrian Fucoid Beds of northwest Scotland. Geological Magazine, 127, 45-53. 
Mckie, T. 1990. Tidal sandbank evolution in the Lower Cambrian Salterella Grit. Scottish Journal of Geology, 26, 77-88. 
Park, E G, Stewart, A D and Wright, D T. 2002. The Hebredean Terrane. 45-80 in the Geology of Scotland. Trewin, N H (Editor). (The Geological Society, London.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable