The BGS Lexicon of Named Rock Units — Result Details

Pentland Formation

Computer Code: PNTL Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Toarcian Age (JT) — Oxfordian Age (JO)
Lithological Description: A complex association of sedimentary (interbedded sandstones, siltstones, mudstones and coals) and volcanic (tuffs, lavas and intrusives) rocks. Beryl embayment: Generally free of volcanics. The formation comprises interbedded sandstones, siltstones and shales with minor coals at the base and top. Sandstones are sharp-based and often fining upwards from coarse- to very fine-grained, sometimes cross-bedded, with occasional parallel lamination and bioturbation in the very fine grained sandstones. Siltstones and mudstones are variable; some are lenticular bedded, others are waxy with blocky fracture, and bioturbation and rootlets are also occasionally present. South and Central Viking Graben: Similar to the Beryl Embayment, but coals occur at numerous horizons. Volcanic and intrusive rocks (Rattray Volcanics Member) occur locally. Outer Moray Firth and Central Graben: Sedimentary rocks are similar to the South Viking Graben, but volcanic and intrusive rocks (Rattray Volcanic and Ron Volcanic members) occur. At the base of the formation, an upward coarsening lacustrine mudstone with a Bathonian microfauna occurs in Well 30/1c-2. The Rattray Volcanics member comprises 1-9 m thick, porphyritic lavas with abundant phenocrysts of olivine and clinopyroxene, microphenocrysts of plagioclase feldspar, and a matrix of plagioclase, titanaugite, magnetite, ilmenite, apatite and rare analcime. Lavas are mainly undersaturated, with alkali olivine basalt affinities, and include ankaramite, alkali olivine basalt, hawaiite and mugearite. Associated agglomerates, tuffs, tuffaceous claystones are varicoloured, pyritic, chloritic, sometimes felsic, calcareous and/or glassy. Sandstones and mudstones are interbedded with the volcanics in places. The Ron Volcanics Member in the southern part of the Central North Sea comprises lavas and intrusives of undersaturated basalts enriched in potassium.
Definition of Lower Boundary: The lower boundary is unconformable. It is marked by a downward change from coal bearing sediments and/or volcanics to evaporite-bearing sediments (Permian); to brick-red siltstones and sandstones (Triassic) or to grey siltstones with minor sandstones (Lower Jurassic).
Definition of Upper Boundary: The upper boundary is characterised by a downward change from sandstones and mudstones (Hugin Formation); mudstones (Heather Formation) or, locally, spiculites (Alness Spiculite Member) to coal-bearing, interbedded sandstones, siltstones, mudstones and/or volcanics.
Thickness: Usually up to 500-550 m, but c. 1500 m in North Sea Well 21/3-3.
Geographical Limits: Beryl Embayment, South Viking Graben, Central Graben, Outer Moray Firth and Unst Basin and eastwards into the Norwegian Sector of the North Sea. North Sea quadrants: 1-2, 9, 13-16, 20-23, 29-30, 210-211.
Parent Unit: Fladen Group (FLDN)
Previous Name(s): Bryne Formation (-5228)
C Sands (-5229)
Coaly Unit (-5230)
Linnhe Formation (-5231)
Middle Beryl Sandstone (-5232)
Parry Sandstones (-5233)
Sliepner Formation (-5234)
Alternative Name(s): Bryne Formation
Sliepner Formation
Stratotypes:
Type Section  North Sea Well 15/17-4 between 2663.5 and 2777.5 m below KB (Deegan and Scull, 1977; revised by Richards et al., 1993). 
Reference Section  North Sea Well 9/13-12 between 3501 and 3584.5 m (Richards et al., 1993). 
Reference Section  North Sea Well 9/19-5A between 3650.5 and 3767 m (Richards et al., 1993). 
Reference Section  North Sea Well 16/18-1 between 3869.5 and 4380.5 m (Richards et al., 1993). 
Reference Section  North Sea Well 29/12-1 between 2846.5 and 3078.5 m (Richards et al., 1993). 
Reference(s):
Fall, H G, Gibb, F G F and Kanaris-Sotiriou, R. 1982. Jurassic volcanic rocks of the northern North Sea. Journal of the Geological Society, London, 139, 277-292. 
Harker, S D, Gustav, S H and Riley, L A. 1987. Triassic to Cenomanian stratigraphy of ther Witch Ground Graben. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 809-818. [Graham & Trotman, London] 
Richards, P C. 1989. Lower and Middle Jurassic sedimentology of the Beryl Embayment, and implications for the evolution of the northern North Sea. Unpublished Ph.D. thesis, University of Strathclyde. 
Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic 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] viii + 219 pp. 
Turner, C C, Richards, P C, Swallow, J L and Grimshaw, S P. 1984. Upper Jurassic stratigraphy and sedimentary facies in the Central Outer Moray Firth Basin, North Sea. Journal of Marine and Petroleum Geology, 1, 105-117. 
Harker, S D, Mantel, K A, Morton, D J and Riley, L A. 1993. The stratigraphy of Oxfordian-Kimmeridgian (Late Jurassic) reservoir sandstones in the Witch Ground Graben, UK North Sea. American Association of Petroleum Geologists Bulletin, 77, 1693-1709. 
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. 
Latin, D M, Dixon, J E and Fitton, J G. 1990. Rift-related magmatism in the North Sea Basin. In: Blundell, D J and Gibbs A D (eds.) Tectonic evolution of the North Sea rifts, 101-144 [Oxford Science Publications]. 
Latin, D M, Dixon, J E, Fitton, J G and White, N J. 1990. Mesozoic magmatic activity in the North Sea Basin: implications for stretching history. In: Hardman, R F P and Brooks, J (eds.) Tectonic events responsible for Britain's oil and gas reserves. Special Publication of the Geological Society, London, No.55, 207-227. 
Vollset, J and DorĂ©, A G. 1984. A revised Jurassic and Triassic lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No.3. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable