Network of Offshore Records of Geology and Stratigraphy

NORLEX

Lyr Formation

Introduction

The term Lyr Formation was introduced by Dalland et al. (1988) for a unit of calcareous mudstones and marls.

Sandstone members have not been formally defined, although rare, isolated, sand units have been identified at Barremian and Hauterivian stratigraphic levels and are predicted to be more widespread in the largely un-drilled deeper sections of the Vøring Basin. The following account concentrates on providing some useful additional information on the stratigraphic and geographic distribution of the formation.

Name

English/ Norwegian and any previous names: informally as "Basal Cretaceous Marl" (Hastings 1987).

Derivatio nominis: From the Norwegian word for the fish species Pollachius pallachius or Pollack (Dalland et al., 1988).

Lithology

The Lyr Formation consists of interbedded marls, calcareous mudstones and mudstones with occasional stringers of limestone. The mudstones are calcareous, grading to marls, and are medium dark grey to light grey or white-light grey, green-grey or red-brown, soft to firm, occasionally moderately hard, blocky to sub-fissile, plastic, amorphous, partly silty and micromicaceous. Non calcareous mudstones may also be present (particularly towards the top of the formation) and these are grey, red brown, firm and blocky. The limestones form subordinate stringers and are white to light grey and hard.

Sample depository

Palynological preparations (organic matter depository)

Type well 6506/12-1: 4 slides from ditch cuttings samples covering the interval 3815 m - 3830 m (Stratlab, RRI and OD preparations) deposited at the Norwegian Petroleum Directorate.

Reference well 6407/1-2: 3 slides covering the interval 3520 m - 3526 m including 2 slides from swc samples at 3520.5 m and 3526 m (Stratlab and LAP preparations) deposited at the Norwegian Petroleum Directorate.

Core photographs

Type well 6506/12-1: no cores taken in this formation.
Reference well 6407/1-2: no cores taken in this formation.

Thickness

The Lyr Formation ranges in thickness from 0.5 m to 444 m.

Regional isochore of the Lyr 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 Lyr Formation

Geographical distribution

The Lyr Formation is regionally extensive but generally less than 100 m thick. It locally reaches a maximum in well 6510/2-1 (444 m) located on the Vega High on the Trøndelags Platform. It also forms a local thick in well 6407/8-1 (272 m) on the Halten Terrace and in block 6608/10 on the Dønna Terrace e.g. 6608/10-9 (226.5 m) The Lyr Formation is either absent or extremely condensed in wells on the Nordland Ridge e.g. 6608/11-2 (0.5m) and has not been penetrated in deep water wells in the Vøring Basin.

Dalland et al. (1988) suggested that the carbonate content is expected to decrease to the west in the Møre and Vøring Basins. The formation consists of very thin limestones with intraformational conglomerates on the eastern part of the Trøndelag Platform (Bugge et al. 1984). Dalland et al. (1988) noted a thin sequence of claystones of Hauterivian to Barremian age subcrop along the eastern part of the Trøndelag Platform. Red-brown oxidized silty claystone found there is also commonly encountered in wells further offshore. Similar sequences are exposed on Andøya and on East Greenland.

Occurrences of formation tops in wells

Type 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 type well: 3836 m - 3812.5 m, 23.5m thickness. Note that Dalland et al. (1988) indicated in an addendum to the report that the base of the Lyr Formation in the type well 6506/12-1 should be 3836 m and not 3835 m as illustrated in their figure 26 in agreement with the type description.

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

Reference well

Well name: 6407/1-2

WGS84 coordinates: N 64°47'50.61, E 07°02'23.76
UTM coordinates: 7187495.23 N 406877.13 E
UTM zone: 32
Drilling operator name: Den norske stats oljeselskap a.s. (Statoil a.s.)
Completion date: 15.05.1983
Status: P & A
Interval of type section & thickness in reference well: 3526 m - 3510 m, 16m thickness.

Reference well 6407/1-2 (click to enlarge)

Upper and lower boundaries

Upper Boundary

The upper boundary of the Lyr Formation is normally defined by a downward change from non-calcareous mudstones of the Langebarn Formation to grey or red-brown mudstones, calcareous mudstones or marls of the Lyr Formation. In both the type and reference wells, Dalland et al. (1988) indicated that this boundary corresponds on wireline logs to a downward increase in gamma ray values and decrease in sonic velocities. This atypical wireline log response is taken to reflect a thin regional interval of early Aptian-late Barremian organic-rich mudstones developed in the upper part of this formation. There is an increase in average sonic velocities in the lower part of the formation, providing potential to subdivide the formation into two units.

Lower Boundary

The base of the Lyr Formation is normally taken at a sharp downward change from marls or calcareous mudstones to dark grey or brown-grey, non-calcareous, organic-rich, mudstones of the Draupne Formation. It is usually well defined on wireline logs and characterised by a marked downward increase in gamma-ray values and decrease in sonic velocities.

Well log characteristics

The log response is generally variable. An informal two-fold subdivision of the Lyr Formation is possible in many wells. At the base, the Lyr unit 1 (L1) is a thin unit with higher sonic velocities and variable gamma ray values that is characterised by calcareous mudstones and marls. The overlying Lyr unit 2 (L2) is characterised by mudstones with a less calcareous content and has lower average sonic velocities. On some operator completion logs, it is this intra-Lyr L1/L2 boundary that has been used to define the top of the formation.

Type seismic section

Biostratigraphy

Limited data are available on the biostratigraphy of the Lyr Formation. In deeper parts of the Vøring Basin the formation is not penetrated by wells and in the type area around blocks 6506/12 and 6407/1 located on the Halten Terrace the Lyr Formation truncated and bounded both above and below by unconformities and represented by a restricted Barremian age. In these wells, the age is based primarily on the benthonic foraminiferal species LO Gavelinella intermedia, LO G. barremiana, LO Marssonella trochus, LO Patellina subcretacea and (in the case of the type well 6506/12-1) the common occurrence of Uvigerinammina moesiana as cavings within the underlying Viking Group. This is confirmed by the Barremian dinocyst marker LO Valensiella magna (Zone 31).

More extensive sections of the Lyr Formation are developed in the Gimsan Basin e.g. 6407/8-1 where the base of the Cromer Knoll Group and Lyr Formation is conformable with the underlying Viking Group. In this well the Lyr Formation is over 450 m thick and contains a relatively complete sequence of Hauterivian and Valanginian dinoflagellate cysts. The base of the Lyr Formation is Early Cretaceous, latest Berriasian - earliest Valanginan age and the oldest markers recorded are the LO S. palmula and LO Endoscrinium pharo associated with an influx of pyritised radiolarians.

Age (revised)

Early Cretaceous, late Berriasian - early Aptian.

Following Gradstein et al. (2004) and the Time Scale Creator (TSC) database the Ryazanian Boreal Stage is partly equivalent to the Valanginian and Berriasian Stages. The revised age differs only slightly from the Valanginian - early Aptian age recorded by Dalland et al. (1988).

Correlation

The only Cretaceous sediments present onshore Norway crop out on the east coast of Andøya and have been described in detail by Dalland (1975, 1979 and 1981). These form an approx. 400 m thick, but truncated and condensed, overall transgressive sequence of shallow marine sandstones and deeper offshore mudstones of the Nybua and overlying Skarstein Formations of Valanginan to Aptian age (Løfaldi and Thusu, 1979; Smelror et al., 2001). These are time equivalent to the deeper offshore mudstones of the Lyr Formation.

In addition, Smelror et al. (2001) described some shallow cores of Middle Jurassic- Early Cretaceous age from the Troms III (Harstad Basin) and Nordland VII offshore areas, northern Norway, and correlated these with the Andøya section. Using the lithostratigraphic scheme devised for the Tromsøflaket, western Barents Sea by Worsley et al. (1988), they assigned the Valanginian - Albian cored sediments to the Klippfisk and Kolje Formations. They noted the condensed calcareous siltstones and nodular limestones of the Klippfisk Formation (Valanginian - Hauterivian age) in core 6814/04-U-02 resemble those of the Lyr Formation. These were interpreted as being deposited over a long time span in a marine environment below wave base. The overlying restricted marine dark-grey pyritic claystones of the Kolje Formation (middle Hauterivian - early Albian age) penetrated in the 7018/07-U-01 and 7018/05-U-01 shallow cores (Troms III) are equivalent to the Skarstein Formation of Andøya and the Lyr and 'lowermost' Langebarn Formations of the deeper Norwegian Sea.

Dalland et al. (1988) correlated the Lyr Formation regionally with the Valhall Formation in the North Sea. Biostratigraphic calibrations in this study suggest that it is equivalent to the Åsgard, Mime and (lower) Sola Formations in the Viking Graben, northern North Sea and Knurr and Kolje Formations in the Barents Sea area.

Depositional environment

The formation was deposited under open marine conditions (Gradstein et al., 1999).

Remarks

The Lyr Formation represents deposition with the K1 sequence of Swieciciki et al. (1998), K10 to K30 sequences of Vergara et al. (2001) and the K10 sequence of Færseth and Lien (2002).

References

Bugge, T., Knarud, R. and Mørk, A. 1984. Bedrock geology on the mid Norwegian Continental shelf. In: Spencer, A. M. et al. (eds), Petroleum Geology of the North European margin. NPD/Graham and Trotman, London, 271-283.

Dalland, A.1975. The Mesozoic rocks of Andøy, northern Norway. Norges Geol. Unders., 316, 271-287.

Dalland, A. 1979. The sedimentary sequences of Andøy, northern Norway - deposition and structural history. Norwegian Sea Symposium, Norwegian Petroleum Society, Tromsø, 26, 1- 30.

Dalland, A. 1981. Mesozoic sedimentary succession at Andøy, northern Norway, and relation to structural development of the north Atlantic area. Canadian Society of Petroleum Geologists Memoir, 7, 563-584.

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.

Hastings, D. S. (1987). Sand-prone facies in the Cretaceous of Mid-Norway. In: Brooks, J. and Glennie, K. (eds). Petroleum Geology of North West Europe, Graham and Trotman, 1065-1078.

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.

Gradstein, F., Ogg, J. and Smith, a. 2004 A Geologic Time Scale 2004. Cambridge University Press. 589 pages.

Hastings, D. S. (1987). Sand-prone facies in the Cretaceous of Mid-Norway. In: Brooks, J. and Glennie, K. (eds). Petroleum Geology of North West Europe, Graham and Trotman, 1065-1078.

Løfaldi, M. and Thusu, T. 1979. Micropalaeontological studies of the Upper Jurassic and Lower Cretaceous of Andøya, Northern Norway. Palaeontology, 22, 413-425.

Smelrør, M., Jacobsen, T., Rise, L., Skarbø, O., Verdenius, J. And Vigram, J.O. 1994. Jurassic to Cretaceous stratigraphy of shallow cores on the Møre Basin Margin, Mid-Norway. Norsk Geologisk Tidsskrift, 74, pp. 89-107.

Smelror, M., Mørk, A., Mørk, M.B.E., Weiss, H. and Løseth, H. 2001. Middle Jurassic - Lower Cretaceous transgressive - regressive sequences and facies distribution off northern Nordland and Troms, Norway. In: Martinsen, O.J. and Dreyer, T. (eds). Sedimentary environments Offshore Norway - Paleozoic to Recent. NPF Special Publication, 10, 211 - 232.

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.

Worsley, D., Johansen, R. and Kristensen, S.E. 1988. The Mesozoic and Cenozoic succession of Tromsøflaket. pp. 42-61. In: Dalland, A., Worsley, D. and Ofstad, K. (eds). A lithostratigraphic scheme for the Mesozoic and Cenozoic succession offshore Mid and Northern Norway. Bulletin of the Norwegian Petroleum Directorate, Bulletin No. 4.

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