Nebbhval Member [new]
Shetland Group,
Nise Formation
Introduction
The Nebbhval Member is a local member of the Nise Formation
characterised by
sandstones and interbedded mudstones of Late Cretaceous, earliest Campanian age
developed in the south-western part of the Vestfjorden Basin. The timing suggests that
the Nebbhval Member is related to the same tectonic episode that introduced the thick
Spekkhogger Member sandstones into the deeper Vøring
Basin. This has been attributed
to the initial phase of Campanian-Paleocene rifting that led to the continental
separation between the North Atlantic and the Norwegian Sea. Whereas the sandstones of
the Spekkhogger Member are considered to have been derived from the north or
northeast, the sandstones of the Nebbhval Member are probably derived from the
Norwegian mainland.
Name
English/ Norwegian and any previous names:
In the type well 6610/3-1, the Nebbhval Member was noted informally as an 'intra Nise
sandstone' by the operator Statoil and is currently indicated as a unit without a
formal name on the NPD fact pages.
Derivatio nominis:
Nebbhval is the Norwegian name for the northern bottlenose whale species Hyperooden
ampullatus. This is a toothed whale up to 10m size that can be found in
increasing numbers in the deeper water areas of the Norwegian Sea around Iceland and
Jan Mayen in addition to west of Svalbard and in the North Atlantic.
Lithology
The Nebbhval Member consists of interbedded sandstones and mudstones.
The sandstones are light olive grey to olive grey, clear to transparent or
translucent quartz grains, fine to medium, occasionally medium or coarse to very
coarse in places, moderately sorted, angular to sub-rounded, white to light grey
matrix, moderate calcareous cement, friable to moderately hard, occasionally micaceous
with common glauconite.
The mudstones are medium dark grey to olive grey, predominantly firm,
moderately hard,
sub-fissile to blocky, micro-micaceous, micro-pyritic, slightly or moderately
calcareous and sandy or silty in parts.
Sample depository
Palynological preparations (organic matter depository)
Type well 6610/3-1: 7 slides from 6 core samples and 1 swc sample covering the
interval 2293.4m - 2318m available at the NPD (Statoil preparations).
Core photographs
Type well 6610/3-1: cores #3 to #5 covering the interval 2292m - 2313.9m.
Thickness
The Nebbhval Member varies in thickness from 24 m, e.g. 6610/3-1 (type section), to
40 m.
Isochore map NEBBHVAL (presently only one data point).
Geographical distribution
The Campanian Nebbhval Member is restricted to the Nordland III area located in the
south-westerly part of the Vestfjord Basin in Quadrant 6610 where it varies from 24m
to 40m based on released well data.
Occurrences of formation tops in wells
Type well
Well name: 6610/3-1
WGS84 coordinates: N 66°55'29.70, E 10°54'06.28
UTM coordinates: 7424470.29 N 583170.4 E
UTM zone: 32
Drilling operator name: Den norske stats oljeselskap a.s.
Completion date: 17.02.1993
Status: Suspended, re-entered later.
Interval of type section (m) & thickness in type well (m):
2306 m (2309.43 m uncorrected core depth) - 2282 m, and 24 m thickness.
Reference well
None designated.
Upper and lower boundaries
Upper Boundary
In the type well 6610/3-1 the top of the Nebbhval Member is taken at a downward change
from mudstones of the Nise Formation to sandstones with
interbedded mudstones. It is
marked on wireline logs by a sharp downward decrease in gamma-ray values and increase
in sonic velocity and resistivity values.
Lower Boundary
The base of the Nebbhval Member is defined by a downward increase in gamma-ray values
and an associated decrease in average resistivity values reflecting the change from
sandstones to mudstones. In the type well, 6610/3-1, there is only a slight increase
in average sonic velocities at 2306 mMD and the downward increase in average density
values is a few metres lower at 2313 mMD.
Well log characteristics
In the type well 6610/3-1 the log character is irregular to serrate reflecting the
heterolithic, interbedded nature of the Nebbhval Member.
Biostratigraphy
The Nebbhval Member is located between the dinocyst markers LCO Trithyrodinium
suspectum and LO Spongodinium 'cristatum' and is earliest Campanian
restricted age (Zone 23).
Deeper in the section is the LO Valensiella reticulata. Within this member is
an influx of Chatangiella bondarenkoi that maybe useful for local correlation.
Planktonic foraminiferal associations are low diversity and characterised by simple,
smooth-walled and long-ranging species Globigerinelloides asperus,
Heterohelix globulosa and Biglobigerinella multispina.
Age
Late Cretaceous, earliest Campanian (Zone 24).
The base of the Nebbhval Member lies close to the Santonian /Campanian boundary.
Correlation
The sandstones and interbedded mudstones of the Nebbhval Member pass laterally into
mudstones of the Nise Formation.
The Nebbhval Member is a time equivalent of the oldest part of the Spekkhogger
Member developed in the Vøring Basin and part of the K85-K90 sequence of
Vergara et al.
(2001) and K70 sequence of Færseth and Lien (2002) and Lien (2005).
These sandstones were probably generated during the same Campanian rifting event
associated with the Spekkhogger Member although they have a different source direction
towards the Norwegian mainland.
Depositional environment
There is limited published data available on the depositional setting of the Nebbhval
Member. The sandstones are interpreted as part of a sand prone slope fan, presumably
with a source from the Norwegian mainland (see palaeogeography of Vergara et
al., 2001 figure 11).
The microfaunas, recovered from cores in the type section 6610/3-1 within this member,
are dominated by abundant, simple, tubular, agglutinated foraminifera e.g.
Rhabdammina
spp. This suggests a deep water, bathyal palaeoenvironment and bottom conditions with
low oxygen.
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.
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.
