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)
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Previous Name(s): |
none recorded or not applicable
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Alternative Name(s): |
none recorded or not applicable
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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 |