The BGS Lexicon of Named Rock Units — Result Details

Tarbert Formation

Computer Code: TARB Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Bajocian Age (JB) — Bathonian Age (JN)
Lithological Description: Grey to brown, relatively massive fine- to medium-grained, locally calcite-cemented sandstone with subordinate, thin siltstones, mudstones and coals.
Definition of Lower Boundary: Usually there is a sharp downward change from micaceous and/or bioturbated sandstone to a more thinly bedded, heterolithic sequence of sandstones, siltstones, mudstones and coal (Ness Formation) and a down-section change to erratic gamma-ray values. Where sandstones of the Tarbert Formation are thin, it is difficult to differentiate that formation from the Ness formation, particularly where there are local facies variations as well. There is usually a coarse-grained lag deposit at the boundary. In the north-eastern part of the East Shetland Basin, the Tarbert Formation rests on the Etive Formation without the intervening and distinctive argillaceous interval between, and the boundary is again difficult to locate.
Definition of Upper Boundary: The boundary is marked by a downward change from grey siltstones with minor limestones (Heather Formation) to sandstones. There is a corresponding down-section decrease in gamma-ray values and an increase in velocity.
Thickness: Up to 75 m.
Geographical Limits: East Shetland Basin in North Sea quadrants 2, 3, 210, 211.
Parent Unit: Brent Group (BRNT)
Previous Name(s): Tarbert Sub-Unit (-5210)
Upper Brent Sandstone Member (-5211)
Alternative Name(s): none recorded or not applicable
Type Section  North Sea Well 211/29-3 between 2633.5 and 2772 m below KB (Deegan and Scull, 1977). 
Reference Section  North Sea Well 211/18a-21 between 3444.5 and 3454.5 m (Richards et al., 1993). 
Reference Section  North Sea Well 2/5-3 between 3350 and 3372.5 m (Richards et al., 1993). 
Reference Section  North Sea Well 3/2-2 between 3566 and 3585 m (Richards et al., 1993). 
Reference Section  North Sea Well 3/9a-2 between 3202.5 and 3277.5 m (Richards et al., 1993). 
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. 
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. 
Bowen, J M. 1975. The Brent Oil-Field. In: Woodland, A W (ed.) Petroleum and the contineental shelf of North-West Europe, 353-361. [Heyden & Son, London] 
Brown, S, Richards, P C and Thomson, A R. 1987. Patterns in the deposition of the Brent Group (Middle Jurassic) UK North Sea. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 899-913. [Graham & Trotman, London] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable