The BGS Lexicon of Named Rock Units — Result Details

Flounder Formation

Computer Code: FLND Preferred Map Code: notEntered
Status Code: Full
Age range: Turonian Age (KT) — Maastrichtian Age (KM)
Lithological Description: The Flounder Formation consists of pale to dark grey, occasionally pink to red, very calcareous mudstones, grading into pale to dark grey argillaceous chalky limestones. Thin beds of white brittle cryptocrystalline limestone are also present. The Flounder Formation has a similar wireline-log signature to the more argillaceous developments of the Mackerel Formation, but is distinguished on the basis of its higher overall gamma values (generally over 30-35 API units).
Definition of Lower Boundary: The base of the Flounder Formation is usually taken at a downward change from mudstones with interbedded argillaceous chalky limestones to cleaner, higher velocity limestones of the Herring Formation. It corresponds to a downward decrease in gamma values and an increase in velocity. On intrabasinal highs, the Flounder Formation locally rests unconformably on Jurassic or older rocks (e.g. Pentland Formation in 15/26a-2).
Definition of Upper Boundary: The top of the Flounder Formation is normally marked by a relatively abrupt downward change from the hard chalky limestones of the Tor Formation to calcareous mudstones with interbedded argillaceous chalky limestones, which are commonly stained pink or red. On wireline logs, the boundary corresponds to a downward increase in gamma values and decrease in velocity.
Thickness: The Flounder Formation is up to 500 m in thickness. Seismic evidence suggests that it broadly onlaps, and becomes very thin over, contemporary structural highs (Gatliff et al., 1994). Andrews et al. (1990) interpreted a significant unconformity or hiatus within the Flounder Formation.
Geographical Limits: The Flounder Formation is confined to the southern part of the South Viking Graben and the extreme north of the Central North Sea.
Parent Unit: Shetland Group (STLN)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 22/01- 2A (Deegan and Scull, 1977, p.27, fig.28): 3198-3605 m (10492-11827 ft) below KB (revised depths). Remarks: highly argillaceous chalky limestones and mudstones that were placed within the Tor Formation by Deegan and Scull are here included within the Flounder Formation. 
Reference Section  North Sea well 16/17- 6: 3249-3590.5 m (10660-11779 ft) (Johnson and Lott, 1993). 
Reference(s):
Andrews, I J, Long, D, Richards, P C, Thomson, A R, Brown, S, Chesher, J A, and McCormac, M. 1990. The geology of the Moray Firth. (London: British Geological Survey.) 
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. 
Gatliff, R W, Richards, P C, Smith, K, Graham, C C, McCormac, M, Smith, N J P, Long, D, Cameron, T D J, Evans, D, Stevenson, A G, Bulat, J, and Ritchie, J D. 1994. United Kingdom offshore regional report: the geology of the central North Sea. (London: HMSO for the British Geological Survey.) 
King, C, Bailey, H W, Burton, C A, and King, A D. 1989. Cretaceous of the North Sea. In: Jenkins, D G and Murray, J W (eds) Stratigraphical atlas of fossil foraminifera, 372-417. Ellis Horwood Limited, Chichester, for the British Micropalaeontological Society. 
Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) 
Johnson, H and Lott, G K. 1993. 2. Cretaceous 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