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Blodøks Formation (new) (Blodøksformasjonen)

(After NPD Bulletin no. 5)

Shetland Group


Named after Eirik Haraldson Bloødks, a Norwegian king who reigned in Norway (A.D. 930-934) and in Northumberland (A.D. -954).

Well type section

Norwegian well 25/1-1 from 3807 to 3790 m, coordinates N 59°53'17.40", E 02°04'42.70". No cores.

Well reference sections

Norwegian well 35/3-2 from 3207 to 3190 m, coordinates N 61°51'O5.98", E 03°46'28.22". No cores.
Norwegian well 1/3-1 from 4371 to 4343 m, coordinates N 56°51'21.00", E 02°51'05.00". No cores.
Danish well BO-1 from 2220 to 2213 m, coordinates N 55°48'02.22", E 04°34'18.66". Cored throughout.


The formation is 17 m thick in the type well (25/1-1), 17 m in well 35/3-2, 28 m in well 1/3-1 and 7 m in well BO-1. It rarely exceeds 20 m in thickness.


The formation consists of red, green, grey and black shales and mudstones which are non-calcareous to moderately calcareous. In the central North Sea the formation may show a varied influx of marls, limestones and chalky limestones.

Basal stratotype

The lower boundary is generally characterised by a distinct log break with an upward increase in gamma-ray intensity and a distinct decrease in velocity from the Svarte Formation (Fig. 33) or Hidra Formation (Fig. 24) into the Blodøks Formation. This is due to the lower content of carbonate in the Blodøks Formation.

Characteristics of the upper boundary

The upper boundary shows a decrease in gamma-ray intensity and an increase in velocity from the Blodøks Formation upwards into the more calcareous Tryggvason Formation or the chalky Narve Formation.

Geographical distribution

The formation is present throughout the North Sea, lacking only on local highs such as the Sørvestlandet High, the Utsira, Mandal, Jæren and Sele highs and the Grensen Ridge as well as above many salt diapirs.

Occurrences of formation tops in wells
Isochore map HIDRA-BLODØKS

Biostratigraphy and Stage/Age

Latest Cenomanian to early Turonian; base taken at the base of UC4 near 94.5 Ma.

Depositional environment

The formation was deposited during a period characterised by anoxic bottom conditions (e.g. Hart & Leary 1989). Presence of carbonates may indicate periods of more oxic conditions or supply of allochthonous limestones and chalks (e.g. Norwegian wells 1/3-1 and 2/5-1).


The Blodøks Formation is equivalent to the former Plenus Marl Formation and the informal "formation B" of Deegan & Scull (1977). A black shale of Early Turonian age is also widespread outside the North Sea, e.g. the Yorkshire Black Band in England (Jeffries 1963) and similar facies on Helgoland and in northwestern Germany (Schmidt and Späth 1980).


Isaksen, D. and Tonstad, K. (eds.) 1989: A revised Cretaceous and Tertiary lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No. 5, 59 pp.

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