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Kvitnos Formation

Shetland Group

Introduction

The Kvitnos Formation was originally introduced by Dalland et al.(1988) for a widespread unit of calcareous mudstones developed below the Nise Formation. Two new sandstone members are defined within this formation: the Tumler Member, an interval of Santonian sandstones in the Vøring Basin, and the Kvitskjæving Member, a unit with a similar stratigraphic age developed in the Vestfjorden Basin.

Name

English/ Norwegian and any previous names: No previous formal or published informal names.

Derivatio nominis: Kvitnos is the Norwegian name for the white-beaked dolphin or Lagenorynchus albirostris. This small (up to 3m long) 'springar-type' species is found in flocks up to 30 individuals over large parts of the north Atlantic, around the British Isles and the Norwegian and Barents Seas, primarily in shallow coastal areas, in contrast to the closely related Kvitskjæving, which is found in deeper waters.

Lithology

The Kvitnos Formation consists predominantly of calcareous mudstones with subordinate carbonate and sandstone stringers (Dalland et al., 1988). The mudstones light-medium grey, green-grey, occasional medium-dark grey, soft, plastic, amorphous, occasional firm to blocky, subfissile, slightly to moderately calcareous and slightly silty. The limestones stringers are grey-white, occasionally light brown, soft to moderately hard, occasionally argillaceous and micritic. The dolomite stringers are light brown to light orange brown, moderately hard to hard. The minor thin sand beds are predominantly loose to cemented, light grey-white, very fine to fine, occasionally coarse, clear translucent quartz, sub-rounded to subangular, sub-spherical, well sorted, and occasionally weakly calcite cemented.

Sample depository

Palynological preparations (organic matter depository)

Type well 6506/12-4: 44 slides (dc and 6 swc) covering the interval 2614 m dc - 3124 m dc (Stratlab, RRI and Saga preparations) deposited at the Norwegian Petroleum Directorate. Note that the four core samples analysed between 3129.1 m-3132.5 m fall within the depth range of the formation but due to a core shift of +5.9 m are part of the Blålange Formation and Lysing Member and have been excluded from this formation (see below).

Reference well 6506/12-1: 75 slides (dc and 2 swc samples) covering the interval 2660 m dc - 3170 m dc (Stratlab, RRI and OD preparations) deposited at the Norwegian Petroleum Directorate.

Core photographs

No cores were taken in the designated type 6506/12-4 and reference 6506/12-1 wells. Note that in the type well 6506/12-4, core#1 (3129 m- 3150.9 m MDRKB) falls within the depth range of the formation but due to a +5.9 m depth shift lies entirely within the Blålange Formation and Lysing Member rather than the Kvitnos Formation.

Thickness

The Kvitnos Formation has a thickness range of 3.5 m to 1108 m.

Regional isochore of the Kvitnos Formation thickness in the Norwegian Sea based on released well data. The isochore map is generated from Norlex data using thin plate splines (thickness constrained to original range). Thicknesses in metres. Circled wells contain both top and base horizons. The red wells have Norlex biostratigraphy. Click for large version.

Interactive Function: Note that this map is only a regional interpretation and the user can generate more specific, local area isochore maps interactively within Norlex using the link below.

Interactive Norlex isochore map for the Kvitnos Formation

Geographical distribution

The formation is laterally continuous in the Vøring Basin and on the Halten-Dønna Terrace areas. The main depositional centres of the Kvitnos Formation are recorded in wells on the structural highs in the Vøring Basin e.g. 6707/10-1 (1108 m at well TD), 6706/11-1 (1037 m), Helland Hansen Dome well 6505/10-1 (933 m) and the Ormen Lange Dome well 6305/1-1 (862m) in the Møre Basin. An anomalously thick interval is developed in the 6507/1-1 well located on the Dønna Terrace where the Kvitnos Formation reaches almost 1000 m. Generally thicknesses decrease on the Halten-Dønna Terrace areas to between 600-150 m. The Kvitnos Formation is, together with other Cretaceous formations, either thin or absent on the Nordland Ridge e.g. 6507/6-1 or on the crest of fault structures on the Halten Terrace such as the Heidrun Field e.g. 6507/7-6 (3.5 m).

Occurrences of formation tops in wells

Type well

Well name: 6506/12-4
WGS84 coordinates: N 65°12'46.97, E 06°43'30.37
UTM coordinates: 7234298.14 N 393591.29 E
UTM zone: 32
Drilling operator name: Den norske stats oljeselskap a.s. (Statoil a.s.)
Completion date: 13.08.1985
Status: P & A
Interval of type section & thickness in type well: 3132.5 m - 2600 m, 532.5 m thickness.

Type well 6506/12-4 (click to enlarge)

Reference well

Well name: 6506/12-1
WGS84 coordinates: N 65°10'07.58, E 06°43'44.07
UTM coordinates: 7229359.52 N 393591.68 E
UTM zone: 32
Drilling operator name: Den norske stats oljeselskap a.s. (Statoil a.s.)
Completion date: 06.02.1985
Status: P & A
Interval of type section & thickness in reference well: 3175 m - 2658 m, 517 m thickness.

Reference well 6506/12-1 (click to enlarge)

Upper and lower boundaries

Upper Boundary

The top of the Kvitnos Formation and the boundary with the overlying Nise Formation reflects a downward change to more calcareous mudstones. This change is marked on logs by a downward decrease in gamma-ray values and an increase in average sonic velocity and density values. Dalland et al. (1988) also noted a corresponding downward increase in resistivity values.

Lower Boundary

The base of the Kvitnos Formation is normally taken at a downward change from calcareous mudstones to non-calcareous mudstones of the Blålange Formation or sandstones of the Lysing Member. It is marked on logs by a downward decrease in average gamma-ray values and increase in average sonic velocity. Dalland et al. (1988) also noted a corresponding downward increase in resistivity values (typically when associated with the underlying Lysing member).

Well log characteristics

The Kvitnos Formation has a relatively uniform profile on gamma-ray logs reflecting the monotonous background deposition of marine mudstones. However, the formation can be sub-divided into a series of regionally correlatable units based on the sonic log. A downward increase in average sonic velocity within the lower part of the formation appears to coincide with the Santonian/Coniacian boundary as defined on biostratigraphy and provides an important regional log feature informally denoted k66 e.g. 6506/12-1 3033 m. This provides log control prior to the penetration of Lysing sandstones. Similarly, higher in the formation at approximately the mid-point, there is another downward increase in average sonic velocity that appears to be close to the early/middle Santonian boundary and is defined as k68 e.g. 6506/12-1, 2950 m. Above this event sonic velocities appear to be more irregular than those in the lower part of the formation and may reflect the increased frequency of sandstones at this level.

Type seismic section

Biostratigraphy

The lower boundary of the Kvitnos Formation is above the Turonian dinocyst markers LO Stephodinium coronatum and Cyclonephelium membraniphorum (Zone 27). The lower part of the Kvitnos Formation is characterised by a marked increase in Heterosphaeridium difficile and Palaeoperidinium pyrophorum.

As indicate above in the well log character, within the Kvitnos Formation are some discrete, regionally identifiable units defined on the sonic log. The Coniacian/Santonian boundary, as defined by the LO Florentina deanei and more reliably, a marked down-section increase in Chatangiella 'spinosa', that is close to the informal surface k66 defined on sonic logs.

The upper boundary of the Kvitnos Formation is close to the (down-section) influx of the planktonic bivalve Inoceramus (Zone 26) and probably reflects a general increase in availability or preservation potential of calcium carbonate within the formation. This is the key event for the definition of the top Kvitnos Formation. The LO Spongodinium cristatum and LO Whiteinella baltica are developed within the basal part of the overlying Nise Formation.

Age

Late Cretaceous, Coniacian to late Santonian. (revised this study).

Dalland et al. (1988) had a slightly broader Turonian - Santonian age range in their definition of the formation. The lower boundary is generally close but above the Turonian/Coniacian stage boundary, i.e. earliest Coniacian, and the upper boundary is broadly coincident with that of the Santonian/Campanian stage boundary within the limits of the available biostratigraphy.

Correlation

The Kvitnos Formation is laterally equivalent to the middle part of the Kyrre Formation developed in the Shetland Group of the northern North Sea and the Thud and upper Narve Formations (formerly part of the Hod Formation) in the Chalk province of the North Sea.

Depositional environment

Open marine, outer shelf - upper bathyal with more open marine circulation than developed during the underlying Blålange and overlying Nise Formations. This is indicated by the increase in calcareous lithologies and floods of planktonic Inoceramus (Gradstein et al., 1999).

Remarks

A thin sandstone unit of early Santonian age is developed in the lower part of the Kvitnos Formation in the Vema Dome well 6706/11-1 (3737 m - 3750 m) and below the Tumler Member. This is retained as an informal unit due to insufficient data but it may represent a significant event in the deeper parts of the Vøring Basin that represent a precursor to the main rifting phase that developed during the Campanian-Paleocene. The Kvitnos Formation represents deposition within the lower part of the K4 sequence of Swiecicki et al. (1998), K80 of Vergara et al. (2001) and the majority of the K60 sequence of Færseth and Lien (2001).

References

Dalland, A., Worsley, D. and Ofstad, K. 1988. A lithostratigraphic scheme for the Mesozoic and Cenozoic succession offshore Mid and Northern Norway. Bulletin of the Norwegian Petroleum Directorate, Bulletin No. 4, 1-65.

Færseth, R. and Lien, T. 2002 Cretaceous evolution in the Norwegian Sea - a period characterized by tectonic quiescence. Marine and Petroleum Geology, 19, 1005 -1027.

Gradstein, F., Kaminski, M.A. and Agterberg, F.P. 1999. Biostratigraphy and paleoceanography of the Cretaceous seaway between Norway and Greenland. Earth-Science Reviews, 46, 27-98.

Swiecicki, T., Gibbs, P.B., Farrow, G.E. and Coward, M.P. 1998. A tectonostratigraphic framework for the Mid-Norway region. Marine and Petroleum Geology, 15, 245-276.

Vergara, L., Wreglesworth, I., Trayfoot, M., Richardsen, G. 2001. The distribution of Cretaceous and Paleocene deep-water reservoirs in the Norwegian Sea basins. Petroleum Geoscience, 7, 395-408.

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