The formation consists of mudstones with occasional limestone beds. Some sandstone beds are found in parts of the Agat Field area, in the northeastern part of the Norwegian North Sea, especially in wells 35/9-3 and 35/6-2. The mudstones are medium grey to grey, silty to calcareous, occasionally Pyrite containing, glauconitic or micaceous. The sandstones are clear to white, and very fine to fine grained.
The lower boundary is defined by an increase in gamma-ray intensity and a decrease in velocity from the Tryggvason Formation into the Kyrre Formation due to changes in carbonate content. The boundary is unconformable on structural highs, usually above the Cromer Knoll Group.
The upper boundary shows a decrease in gamma-ray intensity and an increase in velocity from the Kyrre Formation upwards into the Jorsalfare Formation. This log change is also a result of the higher carbonate content and the presence of basal limestone beds in the Jorsalfare Formation.
Distribution and thickness
The Kyrre Formation is time-equivalent with the Flounder Formation in the western part of the central Norwegian North Sea and the upper part of the Hod Formation in the eastern part (Deegan & Scull 1977). It is also equivalent with the informal "formation D" of Deegan & Scull (1977).
With the exception of the Gullfaks area, the formation is present in the Viking Graben, on the Tampen Spur and the western margin of the Horda Platform of the Norwegian North Sea. The Kyrre Formation is 585 m thick in the type well (25/1-1), 1199 m in well 35/3-2, 521 m in well 24/9-1 and 270 m in well 30/11-3.
Open marine, with estimated paleo-water depths of 600-800 n in the central parts of the Viking Graben and 200-300 m on the surrounding flanks.
After rifting in the Permian, Triassic and Late Jurassic, thermally induced subsidence became focused in the axis of the Søgn Graben, located in the northeastern Norwegian North Sea. The previously formed fault-block topography was filled during the early part of the post-rift period, such that by the Late Cretaceous, the Måløy slope had been transformed into a gently westward-dipping slope (Bugge et al., 2001; Gabrielsen et al., 2001; Jackson et al., 2011). The Cretaceous succession reached a maximum thickness of 800 m (2625 ft) in the axis of the Søgn Graben and was dominated by hemipelagic mudstones and thin carbonates. However, during the Late Cretaceous (Late Turonian), sand supply from the Norwegian hinterland to the east was abundant and resulted in deposition of a series of slope-channel complexes and associated terminal fans that were fed through a series of shelf-edge canyons (Martinsen et al., 1999, 2005; Bugge et al., 2001; Jackson, 2007; Jackson et al., 2008). On seismic data, these sandstone-rich depositional systems are expressed as high-amplitude anomalies, set within a background of predominantly low-amplitude, chaotic reflection events interpreted as hemipelagic mudstones (Jackson et al., 2011).
References in scientific journals and books:
Bugge, T., B. Tveiten, and S. Bäckström, 2001, The depositional
history of the Cretaceous in the northeastern North Sea: Norwegian Petroleum Society Special Publication 10, p. 279–291.
Gabrielsen, R. H., R. Kyrkjebø, J. I. Faleide, W. Fjeldskaar, and T. Kjennerud, 2001, The Cretaceous post-rift basin configuration of the northern North Sea: Petroleum Geoscience, v. 7, p. 137–154.
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.
Jackson, C. A.L., M. Huuse, and Gillian P. Barber, 2011: Geometry of winglike clastic intrusions adjacent to a deep-water channel complex: Implications for hydrocarbon exploration and production. AAPG Bulletin, v. 95, no. 4 (April 2011), pp. 559–584.
Martinsen, O. J., T. Lien, and C. A.-L. Jackson, 2005, Cretaceous
and Paleogene turbidite systems in the North Sea and Norwegian Sea basins: Source, staging area and basin physiographic controls on reservoir development, in A. G. Dore and B. Vining, eds., Petroleum geology of
northwest Europe and global perspectives: Proceedings of the 6th Petroleum Geology Conference, Geological Society (London), p. 1147–1164.