Kai Formation

Nordland Group

Members of Formation

Molo Member | Utsira Member


English/ Norwegian

Kai Formation / Kaiformasjonen

Derivatio nominis

Named from the Norwegian word for quay (Worsley et al. 1988).

Original definition

Worsley, D., Johansen, R. & Kristensen, S.E. 1988. The Mesozoic and Cenozoic lithostratigaphic scheme for the Mesozoic and Cenozoic succession offshore mid- and northern Norway. NPD Bulletin No. 42-61.


The Kai Formation consists of alternating claystone, siltstone and sandstone. Limestone stringers may be present. Glauconite, pyrite and shell fragments are common (Worsley et al. 1988). The sand content varies locally; sandstones of the Utsira Member being distributed in the Viking Graben and sandstones assigned to the Molo Member extending from the coast of Møre up to the Nordland Ridge/Lofoten area. In the Vøring Basin, along the Vøring Marginal High and the Gjallar Ridge strata assignable to the Kai Formation comprise calcareous and siliceous ooze.


The formation comprises 271 m in the type section well 6407/1-2. Major depocentres are in the Vøring and Møre basins where the Kai Formation displays a sheet-form geometry. In the Vigrid Syncline the formation comprise up to 700 milliseconds of sediments (Stoker et al. 2002).

Geographical distribution

The formation is present throughout the Haltenbanken area and the Vøring Plateau. The formation is locally absent from the crest of the Nordland Ridge, and mid-slope structural highs such as the Helland-Hansen Arch, Nyk High and Ormen Lange Dome. Southwards the formation extends into the Northern North Sea region.

Type well

Well name



WGS84 coordinates: 64°47'50.61"N, 07°02'23.76"E
UTM coordinates:
UTM zone: 31

Drilling operator name


Interval of type section (m)

From 1690-1419 m in type section well 6407/2-1.

Thickness in type well (m)

271 m in the type section well.

Reference well

Well name

No reference well for the Kai Formation was described by Worsley et al. (1988). Here we propose well 6607/5-1 as a formal reference well for the formation.


WGS84 coordinates: 66°38'09.67"N, 7°32'21.38"E
UTM coordinates: 7391750.71N, 435359.29E
UTM zone: 32

Drilling operator name

Esso Exploration and Production

Completion date


Interval of reference section (m)

In the reference well the Kai Formation extends from 2082-2448 m (Eidvin et al. 1998).


Lower boundary (basal stratotype)

The base is defined by a decrease in interval transit time on the sonic log and an increase in density log readings (Worsley et al. 1988)

Upper boundary (characteristics)

In the type well 6407/1-2 the top of the Kai Formation is recognized by a marked decrease in interval transit time and gamma response, combined with an increase in resistivity log readings.

Upper and lower boundaries in reference well sections

In reference well 6607/5-1 the lower boundary is at 2448 m (Eidvin et al. 1998), and is marked by an unconformity above the underlying Brygge Formation. The upper boundary corresponds to the transition to the overlying Naust Formation at 2082 m. This boundary also corresponds to an unconformity, where Upper Pliocene deposits of the Naust Formation rests directly on Upper Miocene deposits of the uppermost Kai Formation.

"Reference" seismic sections

Seismic line GMNR-94-106 (Eidvin et al. 1998).

Fossil events/zones dating the formation

Dinocyst biozonation in type well 6407/1-2

1419 mtop of Kai Formation 
1490 mLAD Batiacasphaera spp. 
1510 mLAD Hystrichosphaeropsis obscura= Top L. truncatum Zone
1520 mLAD Spiniferites pseudofurcatus 
1520 mLAD Dapsilidinium pseudofurcatum 
1590 mLAD Palaeocystodinium golzowense= Top P. golzowense Zone
1640 mLAD Cannosphaeropsis passio= Top C. passio Zone
1690 mbase of Kai Formation 

Dinocyst picks in type well 6407/1-2

Investigated interval: 1410 (no recovery) - 1490-1700 m

1490 mLAD Batiacasphaera spp.
1490 mLAD Systematophora ancyrea
1510 mLAD Hystrichosphaeropsis obscura
1510 mLAD Pentadinium laticinctum imaginatum
1510 mLAD cf. Hystrichosphaeropsis variabile
1520 mLAD Spiniferites pseudofurcatus
1520 mLAD Cordosphaeridium cantharellum
1520 mLAD Hystrichokolpoma rigauidae
1520 mLAD Melitashpaeridium choanephorum
1520 mLAD Tectatodinium sp. 2 Manum et al. 1989
1520 mLAD Hystrichostrongylon membraniphorum
1520 mLAD Dapsilidinium pseudofurcatum
1520 mLAD Spiniferites cf. pachyderma
1540 mLAD Impagidinium sp. 4 Manum et al. 1989
1550 mLAD Homotrybilum floripes
1550 mLAD Operculodinium cf. giganteum sensu Manum et al. 1989
1560 mLAD Selenopemphix crenulata
1560 mLAD Tectatodinium simplex
1590 mLAD Palaeocystodinium golzowense
1590 mLAD Lejeunecysta hyaline
1590 mLAD Tuberculodinium vancampoae
1610 mLAD Selenopemphix nephroides
1640 mLAD Cannosphaeropsis passio
1640 mLAD Hystrichokolpoma sp. 1
1640 mLAD Dinocyst IV Manum 1976
1660 mLAD Pyxidiniella? Simplex
1660 mLAD Problematicum IV Manum 1976
1660 mLAD Invertocysta tabulata


The formation is dated as Early Miocene to Late Pliocene (Worsley et al. 1988).

Depositional environment

The Kai Formation was deposited in marine environments with varying water depths. The fine-grained sediments of the Kai Formation were deposited in an outer-shelf environment, while the sandstones of the Utsira and Molo members were deposited in coastal shallow marine environments.


The Kai Formation is here redefined to also include the time-equivalent Utsira and Molo members, implying that the formation also is extended into the North Sea area.

Stoker et al. (2002) suggested that the Kai Formation extends from 1654-2082 m in the reference well 6607/5-1. This is, however, not supported by the present log interpretation and the biostratigraphic correlation provided by Eidvin et al. (1998).


Eidvin, T. Brekke, H., Riis, F. & Renshaw, D.K. 1998. Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64N-68N. Norsk Geologisk Tidsskrift 78; 125-151.

Stoker, M.S. (compiler) 2002: The Neogene stratigraphy of glaciated European margin from Lofoten to Porcupine. STRATAGEM project.

Worsley, D., Johansen, R. & Kristensen, S.E. 1988. The Mesozoic and Cenozoic succession of Tromsøyflaket. In Dalland, A., Worsley, K. & Ofstad, K. (eds.): A lithostratigaphic scheme for the Mesozoic and Cenozoic succession offshore mid- and northern Norway. NPD Bulletin No. 42-61.

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