The BGS Lexicon of Named Rock Units — Result Details

Dornoch Formation

Computer Code: DORN Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Paleocene Epoch (GP) — Eocene Epoch (GE)
Lithological Description: The Dornoch Formation consists of sandstone, siltstone and silty mudstone, with subordinate lignite and claystone in the uppermost part (Beauly Member). The sandstones range from fine to very coarse grade, with local conglomeratic beds, and are generally poorly consolidated. In parts of the Northern North Sea (e.g. block 3/1), the topmost bed of the formation is conglomeratic (Mudge & Copestake 1992). The siltstones and mudstones are brown-grey to grey-brown, micaceous, carbonaceous, and pyritic. They are poorly consolidated and display little or no fissility. Tuffaceous mudstones have been reported from some sections.
Definition of Lower Boundary: The Dornoch Formation generally rests directly on mudstone of the Lista Formation, in which case it is marked by a change from grey, carbonaceous, silty, commonly fissile mudstone to to green-grey or olive-grey, poorly bedded mudstone with abundant agglutinating foraminifera. The associated changes in wireline-log character are somewhat variable, depending on whether the base of the Dornoch Formation is represented by sandstone (e.g. 14/25-1, 21/1-6) or mudstone (e.g. 3/8a-5A, 9/18a-4). However, the lower boundary usually occurs at, or shortly below, a marked downward decrease in sonic velocity.
Definition of Upper Boundary: The Dornoch Formation is variously overlain by grey mudstones of the Sele Formation (e.g. 3/8a-5A, 9/18a-4), grey, silty, tuffaceous mudstones of the Balder Formation (e.g. 14/25-1), or green-grey, silty, glauconitic mudstones of the Mousa Formation or the Horda Formation (e.g. 21/1-6). The boundary is marked by a downward decrease in gamma-ray values, corresponding to a downward change from mudstone to sandstone, siltstone, or lignite. A marked increase in velocity commonly occurs at, or close to, the boundary, but where lignitic beds occur at the top of the formation (e.g. 14/19-5), there is a marked downward decrease in velocity.
Thickness: Reaches over 600 m in the Outer Moray Firth; East Shetland Platform 200-300 m.
Geographical Limits: The Dornoch Formation is present over western parts of the Outer Moray Firth and over much of the East Shetland Platform, extending into the Beryl Embayment and the East Shetland Platform.
Parent Unit: Moray Group (MORA)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  North Sea well 14/25-1 (Deegan & Scull 1977, p.32, fig.38): 1080-1583 m (3544-5193 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 3/8a-5A: 1475.5-1718.5 m (4840-5638 ft). 
Reference Section  North Sea well 9/18a-4: 1812.5-2225 m (5947-7300 ft). 
Reference Section  North Sea well 21/1-6: 1072-1593 m (3517-5226 ft). 
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