| Computer Code: |
MCBT |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Turonian Age (KT)
— Turonian Age (KT) |
| Lithological Description: |
The Macbeth Formation consists of mudstones with interbedded limestones. The mudstones are pale to dark grey, calcareous to non-calcareous and occasionally very silty, micaceous, glauconitic and pyritic. The limestones are chalky and argillaceous, white to pale grey or brownish grey, and locally glauconitic. In the Viking Graben and East Shetland Basin, the limestone units are up to about 60 m thick (e.g. 9/10c-2), but both the proportion of limestone and the thickness of individual limestone beds tend to decrease northwards and away from contemporary structural highs (e.g. 3/10b-1). In the Beryl Embayment and Viking Graben, the formation displays an overall 'barrel-shaped' wireline log signature, with a more calcareous middle section underlain and overlain by more argillaceous deposits (e.g. 9/10c-2).
A unit of relatively high-gamma mudstones at the base of the Macbeth Formation is designated the Black Band. |
| Definition of Lower Boundary: |
The base of the Macbeth Formation is normally marked by a downward change from essentially non-calcareous mudstones (Black Band) to calcareous mudstones and argillaceous chalky limestones of the Svarte Formation (e.g. 3/29-1 and 9/10c-2). It is marked on wireline logs by a decrease in gamma values and an increase in velocity. Commonly, the Black Band is difficult to recognize (e.g. 3/12-2). Over some structural highs, the Macbeth Formation rests unconformably on very condensed sections of the Cromer Knoll Group or on pre-Cretaceous rocks (e.g. Kimmeridge Clay Formation in 9/19-7Z). In the Beryl Embayment and South Viking Graben, the Macbeth Formation overlies the Hidra Formation. |
| Definition of Upper Boundary: |
The top of the Macbeth Formation is normally marked by a downward change from mudstones of the Kyrre Formation to argillaceous chalky limestones and interbedded mudstones. It is marked on wireline logs by a downward decrease in gamma values and an increase in velocity. |
| Thickness: |
The Macbeth Formation is up to 175 m thick in the UK North Viking Graben. |
| Geographical Limits: |
The Macbeth Formation occurs in the UK Viking Graben, Beryl Embayment and the south and west of the East Shetland Basin. It is, however, absent over contemporary structural highs. Seismic evidence suggests onlap of the formation onto these structures, but condensation and intra-Cretaceous erosion may also be a limiting factor (Johnson et al., 1993). |
| 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 3/29- 1: 3603-3778 m (11821-12395 ft) below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 3/10b- 1: 35 86-3 840 m (11765-12598 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.) |
| Abbotts, I L (ed.) 1991. United Kingdom oil and gas fields 25 years commemorative volume. Geological Society, London, Memoir No. 14. |
| 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 |
| Johnson, H, Richards, P C, Long, D, and Graham, C C. 1993. United Kingdom offshore regional report: the geology of the northern 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. |
| Ritchie, J D, Gatliff, R W and Riding, J, 1996. 1. Pre - Tertiary lithostratigraphy. In: Stratigraphic Nomenclature of the UK North West Margin. British Geological Survey, Nottingham. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
