Skrubbe Member (Skrubbeleddet)
Shetland Group,
Blålange Formation
Introduction
The Skrubbe Member is a new member of Blålange Formation
(new herein) and is a
interval of lower Turonian sandstones found locally in the Vestfjorden Basin.
Name
English/ Norwegian and any previous names:
Described informally as the 'Lange sandstone 1' by the operator Statoil and
indicated as a unit with no formal name in the type well
6610/3-1 R
on the NPD fact pages.
Derivatio nominis:
The name Skrubbe is Norwegian for the flounder fish species Platichthys
flesus.
This flatfish is usually found living on muddy bottoms in shallow depths of
0-75m along the whole of the Norwegian coastline and in the fjords.
Lithology
The Skrubbe Member consists of interbedded sandstones and claystones with
occasional thin stringers of limestone and dolomitic limestone especially
developed in the lower part.
The sandstones are light to medium dark grey, with clear to translucent
grains,
fine to coarse, occasionally very coarse, poor to moderately sorted, sub-angular
to sub-rounded, friable to moderately hard, calcareous cement or occasionally
abundant argillaceous matrix, micaceous, glauconitic, carbonaceous in part,
with poor to no visible porosity, occasionally grading to sandy claystone.
The claystones are medium dark grey to olive black, blocky to
sub-fissile,
moderately hard, silty or sandy in parts, micro-micaceous to very micaceous in
parts, occasional micro-pyrite, trace carbonaceous material, predominantly
slightly to non calcareous.
Occasional thin stringers of limestone or dolomitic limestone throughout
this
unit are greyish white to light brown, soft to hard, blocky, micro-crystalline,
argillaceous, occasionally glauconitic, sandy and silty in parts grading to
calcareous sandstone.
Basal stratotype
The base of the Skrubbe Member is defined by a decrease in gamma ray log
response and an increase in resistivity values in response to the up-section
development of sandstones. There is an associated weak decrease in interval
transit times but overall, both the gamma ray and sonic log values are more
irregular than the underlying mudstones.
Sample depository
Palynological preparations (organic matter depository)
Type well 6610/3-1 R:
12 slides including 9 sidewall core samples deposited at
the NPD covering the interval 2890m swc - 3040m swc (Statoil and RRI
preparations).
Core photographs
Type well 6610/3-1 R:
no cores were taken in this member.
Thickness
The Skrubbe Member is less than 170 m thickness.
Geographical distribution
The Skrubbe Member is locally developed in the Vestfjorden Basin.
Type well
Well name: 6610/3-1 R
Location
WGS84 coordinates: N 66°55'29.70, E 10°54'06.28
UTM coordinates: 7424470.29 N 583170.04 E
UTM zone: 32
Drilling operator name: Den norske stats oljeselskap a.s
Completion date: 11.12.1993
Status: suspended, re-entered later.
Interval of type section (m) & thickness in type well (m):
3047m - 2884m and 163m thickness.
Reference wells
Not designated
Upper and lower boundaries (in paratype section if type well is
insufficient)
Well log characteristics [Figure]
The Skrubbe Member is characterised by a serrate profile on gamma ray logs in
response to the sandstone - claystone interbedded nature of the unit. Sandstone
beds are more frequent in the upper part of the member although these never
exhibit large scale, blocky log profiles.
Some sandstones show gradational (fining upward) profiles with the overlying,
thinner mudstone interbeds.
Type seismic section
Location: ST 9104-437 and SP. 335 (well 6610/3-1R)
Section
Biostratigraphy
The Skrubbe Member is developed between the dinocyst events LCO
Cyclonephelium
membraniphorum, LO Cribroperidinium edwardsii (early Turonian) and
the LO (few)
Litosphaeridium siphoniphorum (Cenomanian). The Turonian restricted FO
Heterosphaeridium difficile occurs in swc in the upper part of this
member.
Reworking of Albian - Cenomanian dinocysts is probably the result of reworking
of the underlying sediments from up-slope locations.
Small,smooth planktonic foraminifera are frequent in the underlying Cenomanian
claystones, mainly Hedbergella delrioensis and H. planispira but
are generally
rare or poorly preserved and pyritised in the Turonian interval associated with
the Skrubbe Member.
Age
Late Cretaceous, early Turonian.
Correlation
The Skrubbe Member is developed in the lowermost part of sequence K50 of Færseth
and Lien (2002). In the type well
6610/3-1 R
the early Turonian Skrubbe Member
lies between the Sandflyndre Member (Cenomanian) and
Lysing Member (Coniacian).
Depositional environment
There are limited available data on the depositional setting of this member and
cores are lacking. The sandstones are considered to be derived by gravity flow
processes into a relatively deep marine, slope or local sub-basinal
palaeoenvironment. An upper bathyal, slope setting is indicated by the prevalence
of low diversity, deep water agglutinated foraminifera (DWAF) in the microfaunas of
the adjacent mudstones. The general lack of calcareous taxa suggests a reducing
sub-oxic bottom environment. The base of the Skrubbe Member in the 6610/3-1R well
is considered to be a minor stratigraphic break and probably the result of erosion
of the underlying sediments during deposition.
Remarks
References
Færseth and Lien (2002)
