updated to follow: Stratigraphic Guide to the Cromer Knoll, Shetland and Chalk Groups of the North Sea and Norwegian Sea. Felix M. Gradstein & Colin C. Waters (editors), Mike Charnock, Dirk Munsterman, Michelle Hollerbach, Harald Brunstad, Øyvind Hammer & Luis Vergara (contributors). Newsletter on Stratigraphy, vol 49/1 pp71-280, 2016
Shetland Group, Northern North Sea
The term Macbeth Formation was introduced by Johnson & Lott (1993) for a unit of interbedded mudstones and argillaceous chalky limestones that lies between the Svarte and Kyrre formations in the UK Viking Graben and East Shetland Basin (see Table). The Macbeth Formation comprised the informal 'Formations' B and C of the Shetland Group (Table 1) as defined by Deegan & Scull (1977). In the Norwegian North Viking Graben, Isaksen & Tonstad (1989) included laterally equivalent strata in the BlodГёks and Tryggvason formations (see Table).
After the 10th century Scottish king.
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, Panel 2, Johnson & Lott, 1993), 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-I, Panel 1, Johnson & Lott, 1993). 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, Panel 2, Johnson & Lott, 1993).
The Macbeth Formation is up to 175 m thick in the UK North Viking Graben (Johnson & Lott, 1993).
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).
WGS84 coordinates: Lat. 60º 06’ 46.5”N; Long. 01º 44’ 21.9”E
UTM zone: 31
Drilling operator name: BP Exploration Operating Company Limited
Completion date: 31.08.1973
Status: P & A
Interval of type section & thickness in type well: 3603-3778 m (11821-12395 ft) below KB (Johnson & Lott, 1993).
|3/10b-1: 3586-3840 m (11765-12598 ft)
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 (Johnson & Lott, 1993).
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 & 9/10c-2, Panel 2, Johnson & Lott, 1993). 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, Panel 2, Johnson & Lott, 1993). In the Beryl Embayment and South Viking Graben, the Macbeth Formation overlies the Hidra Formation (Johnson & Lott, 1993).
The upper boundary is marked on wireline logs by a downward decrease in gamma values and an increase in velocity into the Macbeth Formation. The lower boundary 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, Panel 2, Johnson & Lott, 1993).
Calcareous benthonic foraminifera such as Valvulineria gracillima, Stensioeina pokornyi and Gavelinella intermedia are common. Planktonic taxa are less common, but provide the Praeglobotruncana stephani biomarker; other taxa present include the long-ranging taxa Dicarinella hagni and Praeglobotruncana gibba. The Litosphaeridium siphoniphorum dinoflagellate cyst biomarker occurs in the lower part of the formation, immediately above the Black Band. Acme occurrences of Heterosphaeridium difficile are characteristic of the formation (Costa & Davey, 1992).
?Early to mid Turonian.
The Macbeth Formation is laterally equivalent to the Herring Formation of the South Viking Graben and Central North Sea (see Table)
According to King et al. (1989), the foraminiferal assemblages in the Macbeth Formation (Zone FCN 14a) are dominated by non-calcareous agglutinates, indicating a relatively restricted, sublittoral and bathyal, marine environment.
A unit of relatively high-gamma mudstones at the base of the Macbeth Formation is formally designated the Black Band (Johnson & Lott, 1993). In the East Shetland Basin, the upper part of the Macbeth Formation has been informally designated the 'Basal Shetland Limestone' in several published accounts describing oilfields in the East Shetland Basin (see Abbotts, 1991).