Network of Offshore Records of Geology and Stratigraphy

NORLEX

Tunge Member [new]

Introduction

The Tunge Member is introduced for a unit of interbedded sandstones, mudstones and siltstones of Coniacian age within the upper part of the (new) Blålange Formation. Sandstones of this member are found in the Rås Basin and Slørebotn sub-basin in blocks 6306/10 and 6305/12 on the eastern margin of the Møre Basin. The Tunge Member is therefore geographically distinct but a time equivalent to the Lysing Member developed on the Halten-Dønna Terraces along the western margin of the Trøndelags Platform. In the absence of cores there is limited detailed published data on the depositional setting of the Tunge Member. Regional seismic mapping suggests this member is part of a sand-prone slope apron system developed on the eastern margin of the Møre Basin with the unit representing slope fans derived from an easterly, up-dip source area on the Frøya High or possibly locally derived slumped debris flow units from the Gossa High.

Name

English/ Norwegian and any previous names: In the type well 6306/10-1 the Tunge Member is noted on the NPD fact pages as a unit without formal name within the Kvitnos Formation. The operator Norske Shell referred to the unit informally as a 'Senonian sandstone unit'.

Derivatio nominis: The name Tunge is derived from the Norwegian for the common sole fish species Solea solea. The fish is usually found in numbers in the North Sea and northwards to Trondheimsfjorden, living on muddy bottoms from the littoral zone down to 150m depth and having a habit of migrating upwards through the water mass at night.

Lithology

The Tunge Member consists of interbedded sandstones, mudstones and siltstones. The sandstones are white - light grey to green, very fine to fine grained, with clear to translucent quartz grains, sub-angular, moderate to well sorted, firm to very hard, generally weakly cemented or occasionally with calcareous cement, abundant glauconite and with poor visual porosity.

The mudstones are light grey to dark greenish grey, moderately soft to firm, blocky to sub-blocky, non-calcareous and slightly micaceous.

The siltstones are medium dark grey, firm to moderately hard, blocky, micromicaceous and non-calcareous.

Basal stratotype

The base of the Tunge Member is characterised by a transitional change from sandstones and interbedded mudstones to more uniform mudstones of the underlying Blålange Formation. In the type well 6306/10-1, this boundary is defined at 1858mD RKB by a gradational but still marked downward increase in gamma-ray values and decrease in density logs representing the deepest few thin sandstone beds. The decrease in sonic velocity and positive separation between neutron porosity and density logs is slightly higher in the section at 1851.5mMD and represents the base of the sand-rich interval.

See below for a complete description of both the lower and upper boundaries and well log characteristics of the Tunge Member.

Sample depository

Palynological preparations (organic matter depository)

Type well 6306/10-1: There are no palynological slides are available at the NPD for the type well covering the interval of this member.

Reference well 6305/12-1: Three sidewall cores (Hydro preparations) are available at 2608 m, 2632 m and 2646 m at the NPD covering the unit, upper and lower boundaries of the member.

Core photographs

Type well 6306/10-1: no cores were taken in this member.

Reference well 6305/12-1: no cores were taken in this member.

Thickness

The Tunge Member varies in thickness from 10 m to 33 m.

Interactive Norlex isochore map for the Tunge Member

Geographical distribution

The Tunge Member is developed on the eastern margin of the Møre Basin in quadrants 6205, 6305 and 6306 in the Rås Basin and Slørebotn sub-basin around the Gossen High. It is presumably sourced from the Norwegian mainland to the east or locally from structural highs in the area. Its thickest development is in the type well 6306/10-1.

Occurrences of member tops in wells

Type well

Well name: 6306/10-1

WGS84 coordinates: N 63°09'26.32", E 06°19'41.45"
UTM coordinates: 7006088.05 N 365416.35 E
UTM zone: 32
Drilling operator name: A/S Norske Shell
Completion date: 17.12.1990
Status: P & A
Interval of type section (m) & thickness in type well: 1858 m - 1825 m, 33 m thickness.

Reference well

Well name: 6305/12-1

WGS84 coordinates: N 63°01'25.73", E 05°47'23.94"
UTM coordinates: 6991476.94 N 641178.97 E
UTM zone: 31
Drilling operator name: Norsk Hydro Produksjon AS
Completion date: 18.09.1991
Status: P & A
Interval of reference section (m) & thickness in reference well: 2642 m - 2616 m, 26 m thickness.

Upper and lower boundaries

Lower boundary

The base of the Tunge Member is characterised by a transitional change from sandstones and interbedded mudstones to more uniform mudstones of the underlying Blålange Formation. In the type well 6306/10-1, this boundary is defined at 1858mD RKB by a marked but gradational but still marked downward increase in gamma-ray values and decrease in density logs representing the deepest few thin sandstone beds. The decrease in sonic velocity and positive separation between neutron porosity and density logs is slightly higher in the section at 1851.5mMD and represented the base of the sand-rich interval.

Upper boundary

In the type well 6306/10-1, the top of the Tunge Member is taken at a downward change below a thick interval of mudstones with subordinate limestone stringers within the Kvitnos Formation into an interbedded sequence of sandstones and mudstones. The change is sharp and the upper boundary is defined by a marked decrease in gamma-ray values and increase in sonic velocity. There is also an associated pronounced negative separation on neutron porosity and density logs in response to rapid termination of sandstones.

Well log characteristics

In both the type well 6306/10-1 and the reference well 6305/12-1, the Tunge Member is characterised by an irregular to serrate gamma-ray log profile that is either funnel-shaped or sharp in the lowermost part of the member. This reflects the heterolithic nature of the interbedded sandstone and mudstone sequence.

Type seismic section

NMI-822 & SP. 380

Biostratigraphy

The Tunge Member is developed between the Coniacian dinocyst markers LO Florentinia deanei, LAO Chatangiella 'spinosa' and LCO Heterosphaeridium difficile and late Turonian marker LO Stephodinium coronatum. The member is therefore Coniacian age (Zone 26). In the type well 6306/10-1 planktonic foraminifera are particularly common below the Tunge Member and are represented by mainly smooth, simple-types. The LAO Hedbergella delrioensis is typical of an age no younger than late Turonian. The member contains few planktonic species but LO Archaeoglobigerina cretacea is recorded in the overlying mudstones of the Kvitnos Formation.

Age

Late Cretaceous, Coniacian (Zone 26).

Correlation

The interbedded sandstones and mudstones of the Tunge Member pass laterally into mudstones of the Blålange Formation.

The Tunge Member is a time equivalent of the Lysing Member of the Halten-Dønna Terrace area and therefore part of the K80 sequence of Vergara et al. (2001), K60 sequence of Færseth and Lien (2002) and Lien (2005) and K72 sequence of Fugelli and Olsen (2005a).

Depositional environment

There is limited detailed published data on the depositional setting of the Tunge Member. Vergara et al. (2001) in their regional seismic mapping study of the Norwegian Sea included these sandstones within their K80 sequence in an area of the eastern Møre margin forming part of a slope apron system. This was characterised by sand-prone slope fans derived from an easterly, up-dip source area on the Frøya High or possibly as locally derived slumped debris flow units from the Gossa High and other local emergent structures (see their figure 10).

In terms of the benthic foraminiferal biofacies, both the type and reference wells are characterised by low diversity deep water agglutinated foraminifera (DWAF), primarily tubular Rhabdammina-Haplophragmoides spp. and pyritised microfossils that is consistent with a depositonal setting on a palaeo-slope and suggest dysoxic bottom conditions. The marine microplankton is characterised by high diversities (22 - 26 species/sample) suggesting a fully marine setting.

Remarks

The Tunge sandstones, located in the Rås Basin and Slørebotn sub-basin on the eastern margin of the Møre Basin are inferred to have a different source provenance than those of the Lysing Member, being derived locally and eastwards from the Norwegian mainland.

References

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.

Fugelli, E. and Olsen T. R. 2005a. Screening for deep-marine reservoirs in frontier basins: Part 1 - Examples from offshore mid- Norway. AAPG Bulletin 89(7):853-882.

Lien, T. 2005. From rifting to drifting: effects on the development of deep-water hydrocarbon reservoirs in a passive margin setting, Norwegian Sea. Norwegian Journal of Geology 85:319-332.

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.

home	previous page