| Computer Code: |
MCKL |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Turonian Age (KT)
— Maastrichtian Age (KM) |
| Lithological Description: |
The Mackerel Formation consists of white, pale grey, and occasionally pink or red, fine-grained, and commonly argillaceous chalky limestones. Sections with relatively high amounts of detrital clay are reflected in higher gamma values and lower velocity. The formation becomes more argillaceous towards the South Viking Graben, where it grades laterally into the Flounder Formation. |
| Definition of Lower Boundary: |
The base of the Mackerel Formation is usually taken at a downward change from 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. Commonly, the Mackerel Formation displays a progressive downward decrease in gamma values and increase in velocity immediately above the Herring Formation (e.g. 14/20-6A; 21/4-1). |
| Definition of Upper Boundary: |
The top of the Mackerel Formation is normally marked by a relatively abrupt downward change from the hard chalky limestones of the Tor Formation to 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 a decrease in velocity. |
| Thickness: |
In depocentres, the Mackerel Formation is between 200 and 500 m thick. |
| Geographical Limits: |
The Mackerel Formation is present over much of the Central North Sea. It onlaps and covers the intrabasinal ridges, such as the Jaeren High, but is absent from the highest parts of the Forties-Montrose High and the Western Platform, where it borders the Central Graben. |
| Parent Unit: |
Chalk Group (CK)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 30/19- 1: 3322-3577 m (10899-11735 ft) below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 13/28- 2: 1212.5-1405.5 m (3978-4611 ft) (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 14/20- 6A: 2324-2751 m (7624-9025 ft) (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 29/04a- 1A: 3605-3801 m (11827-12470 ft) (Johnson and Lott, 1993). |
| Reference(s): |
| 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. |
| 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.) |
| 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. |
| Isaksen, D and Tonstad, K. 1989. A revised Cretaceous and Tertiary lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No.5 |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
