The BGS Lexicon of Named Rock Units — Result Details

Beauly Member

Computer Code: BEAU Preferred Map Code: notEntered
Status Code: Full
Age range: Eocene Epoch (GE) — Eocene Epoch (GE)
Lithological Description: The Beauly Member consists of a complex association of sandstone, mudstone and lignite. The sandstones are moderately to well sorted; they are of fine, medium or coarse sand grade, and locally pebbly. They typically display blocky log profiles, though in some sections the gamma-ray trace indicates upward-coarsening units (e.g. 20/10a-3). The lignites are brown to black, generally pure, but occasionally contaminated by detrital mudstone, as indicated by relatively high gamma-ray values. They can be identified on wireline logs by a characteristic association of low gamma-ray values, low sonic velocity and moderate to high resistivity. Individual lignite beds often overlie thin, low velocity claystones, from which they are differentiated by the contrast in gamma-ray values. The lignites are commonly between 2 and 10 m thick, exceptionally reaching over 15 m (e.g. 8/27a-1). The mudstones are variably silty, grading locally into pure claystones. They are mostly pale grey to pale brown, but also include pale grey-green and distinctive blue-green varieties. They contrast with the medium grey-brown, carbonaceous, muddy siltstones associated with the underlying Upper Dornoch Sandstone. Highly altered tuffaceous material is recorded from some sections. Siderite spherulites, presumably associated with claystone units, are locally abundant.
Definition of Lower Boundary: Where one or more thick lignite beds are present, the base of the Beauly Member corresponds either to the base of the lowest lignite (e.g. 14/19-5) or the base of a persistent claystone that locally underlies the lignite. In sections where lignites are thin or absent, the base of the member is marked by a downward change in mudstone character from generally pale and variegated mudstone and claystone to medium grey-brown, carbonaceous, muddy siltstone. In 20/10a-3, an association of thin lignites with pale claystone units allows the base to be drawn with some certainty; here it also coincides with the top of a more consistently sandy section. In other wells it may be appropriate to draw the boundary below the lowest lignite if cutting descriptions indicate the presence of Beauly-type mudstones beneath (e.g. 20/2-7, 20/4-1). Although lignite is normally restricted to the Beauly Member, a thin lignite has been recorded within the Upper Dornoch Sandstone near its western limit (15/3-1). The absence of associated mudstone differentiates this lignite from those of the Beauly Member.
Definition of Upper Boundary: The top of the Beauly Member is marked by a sharp downward change to sandstone or lignite from grey-green, glauconitic, silty mudstone of the basal Stronsay Group (Horda or Mousa Formation) (e.g. 14/19-5, 20/10a-3) or grey, tuffaceous, silty mudstone of the Balder Formation (e.g. 14/25-1).
Thickness: Reaches over 200 m in the southeastern part of Quadrant 14.
Geographical Limits: The Beauly Member is restricted to the Outer Moray Firth area and to southern parts of the East Shetland Platform.
Parent Unit: Dornoch Formation (DORN)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 14/25- 1 (Deegan and Scull, 1977, p.33, fig.38): 1080-1165 m (3544-3822 ft) below KB (revised depths). Depths are based on the gamma-ray log; original sonic log depths have been adjusted by c. 8 ft. 
Reference Section  North Sea well 14/19- 5: 688-861.5 m (2257-2826 ft) (Knox and Holloway, 1992). 
Reference Section  North Sea well 20/10a- 3: 925-1107 m (3035-3632 ft) (Knox and Holloway, 1992). 
Reference(s):
Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. 
Knox, R W O'B and Holloway, S. 1992. 1. Paleogene 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable