Sample photos and petrographic descriptions of core
samples from the Norwegian continental margin basement
Appendix 1
Petrophysical and thermal properties of pre-Devonian basement rocks on the
Norwegian continental margin
Trond Slagstad, Cécile Barrére, Børre Davidsen, Randi K. Ramstad
16/1-4, 1937m—Utsira High, North Sea
Medium- to coarse-grained, undeformed gabbro consisting of roughly equal amounts
of amphibole+biotite and strongly saussuritised plagioclase. The amphibole is
typically partly altered to biotite. Small, calcite-filled veins and vugs are common
16/3-2, 2017.7m—North Sea
Medium-grained, red granite consisting of fine-grained, whitish-red to red feldspar
and coarser (<1 cm) irregular, but generally rounded, grains of quartz. The granite is
unfoliated and spotted with 1–2 mm specks of biotite and muscovite, homogeneously
distributed in the rock.
16/4-1, 2907.4m—Utsira High, North Sea
Compositely layered, fine-grained, light grey impure quartzite and dark grey siltstone.
Layer thickness varies from ca. 1 mm up to several cm. The quartz-rich layers are
rich in epidote, whereas biotite and feldspar dominate in the 'silty' layers. The mineral
assemblage indicates low-grade metamorphism. The sample is criss-crossed by thin,
calcite-filled vein, dominantly subvertical although subhorizontal veins are also
found. The subvertical veins appear to form en echelon patterns, and some of the
veins are only developed in the quartzite but are not visible in the siltstone. This
effect is most likely caused by differences in rheology of the two rock types. Some
cm-thick, green to orange layers, slightly oblique to the layering in the rock appear to
consist of epidote and albite (?) and are most likely metasomatic.
16/4-1, 2908.6m—Utsira High, North Sea
Fine-grained granite, grey with a reddish hue. The granite is unfoliated with 1–3 mm
specks of biotite and minor muscovite, homogeneously distributed in the rock.
16/5-1, 1929.3m—Utsira High, North Sea
Fine-grained, unfoliated, dark red granite with scattered 1–3 mm specks of biotite and
muscovite, homogeneously distributed in the rock. There are some cracks in the
sample with discontinuous, thin, bleached margins, indicating some alteration.
16/6-1, 2059.7m—Utsira High, North Sea
Fine-grained, undeformed, grey volcanic rock with abundant small (<2 mm)
phenocrysts of plagioclase in a fine-grained, feldspar+chlorite+quartz groundmass.
The rock also contains a small (ca. 4 cm) inclusion of slightly coarser grey rock,
probably a xenolith.
17/3-1, 2849.5m—Stord Basin, North Sea
Dark green fault breccia with abundant calcite-filled veins and vugs. The fine-grained
matrix consists mainly of chlorite.
From NPD's Fact-page: "…drilled […] in metamorphic basement rock, dated 410
My".
17/3-1, 2850.7m—Stord Basin, North Sea
Fault breccia consisting predominantly of medium-grained, strongly undulatory
quartz and calcite, typically forming irregular veins in a fine-grained quartz+feldspar
matrix with some chlorite.
18/11-1, 2082.3m—Stavanger Platform, North Sea
Dark green, volcanic rock with plagioclase phenocrysts, typically 1–2 mm across with
a prismatic, rounded to angular shape, set in a fine-grained, quartz+feldspar matrix.
The rock is criss-crossed by numerous, white, hairline veins that locally are calcitefilled.
25/7-1S, 3548.2m—North Sea
Breccia with irregular fragments typically ca. 5 cm long of a dark red, fine-grained
rock, consisting mainly of opaque minerals and calcite. The fragments have slightly
rounded edges.
25/7-1S, 3554.3m—North Sea
Faintly banded, fine-grained, grey metasandstone. The metasandstone consists
mainly of undulatory quartz, with lesser amounts of altered feldspar (mainly Kfeldspar), and prismatic muscovite oriented parallel to the foliation in the rock. The
faint banding represents variation in the proportions of these minerals. Chlorite is an
accessory phase. The metasandstone is criss-crossed by numerous thin veins, with
dark green, white or brown, calcareous infilling.
25/11-17, 2259.5m—Balder/Grane area, North Sea
Microcrystalline to fine-grained, dark brown to grey metasiltstone consisting mainly
of quartz, feldspar and biotite, with minor muscovite and calcite. The rocks are crisscrossed by numerous short (<2 cm), irregular veins and vugs filled with white calcite
and red zeolite.
35/3-4, 4088.3m—North Sea
Fine-grained, dark grey biotite gneiss. The biotite gneiss consists mainly of quartz,
K-feldspar and plagioclase, with rather abundant biotite forming a well-defined
foliation in the rock. Epidote constitutes several percent of the rock, and is typically
enriched in the more biotite-rich layers. Concordant, mm-sized patches and veins of
medium-grained quartz are common. The rock contains a fair amount of pyrite, some
with well-developed crystal faces, typically 1–2 mm across but locally up to 5 mm.
35/9-1, 2313.6m—North Sea
Fine-grained, dark green breccia consisting of fine-grained chlorite and calcite.
Colour varies from light grey, green, dark green to dark grey, giving the rock a
speckled appearance. The breccia contains some mm-thick, calcite-filled veins. No
larger clasts can be observed.
36/1-1, 1588.7m—North Sea
Fine-grained, grey, biotite-epidote-bearing granitic gneiss. Abundant biotite laths
impart the gneiss with a strong foliation.
Note that the indicated sample depth in the photo label is in feet, not metres.
6305/12-2, 3158.3m—Norwegian Sea
Grey fault(?) breccia consisting dominantly of angular fragments of a fine-grained
chlorite+feldspar+calcite rock, separated by thin calcite veins. Numerous calcitefilled veins and vugs. .
6306/10-1, 3158.5m—Frøya High, Norwegian Sea
Medium-grained, unfoliated quartz diorite consisting of sassuritised plagioclase,
hornblende that is commonly partly or completely altered to chlorite, and minor
quartz and epidote. A few calcite-filled cracks are present.
6306/10-1, 3159.2m—Frøya High, Norwegian Sea
Medium-grained, unfoliated quartz diorite consisting of sassuritised plagioclase,
hornblende that is commonly partly or completely altered to chlorite, some quartz and
minor epidote. A few calcite-filled cracks are present.
6407/10-3, 2972.1m—Norwegian Sea
Medium-grained, unfoliated, dark red granite with small specks (<1 mm) of biotite.
6609/7-1, 1944.7m—Norwegian Sea
Breccia with angular, mm- to cm-size fragments of fine-grained, reddish grey, quartzrich metasandstone. The metasandstone contains several percent elongate muscovite
which forms the foliation in the rock, and minor amounts of calcite. The matrix
between the fragments consists of crumbly, microcrystalline, green material, and
minor amounts of red to brown calcareous material.
6609/7-1, 1945.8m—Norwegian Sea
Laminated metasiltstone consisting of layers, typically < 1 cm thick, of fine-grained,
quartz-rich metasiltstone with a orange hue, and thinner layers of grey, muscovite-rich
metasiltstone. The rock is extensively cracked with calcite-filled veins.
7120/1-1, 4002.2m—Loppa High, Barents Sea
Fine-grained, foliated, amphibolite, consisting mainly of amphibole and calcite, with
minor titanite.
7120/2-1, 3478.0m—Loppa High, Barents Sea
Diabase.
7120/2-1, 3479.0m—Loppa High, Barents Sea
Diabase.
7120/12-2, 4675.8m—Norwegian Sea
Dark grey mylonititc, granitic augen gneiss, with numerous thin (<1 mm) and some
thicker (<1 cm) leucocratic veins, concordant with the foliation in the rock.
7120/12-2, 4678.2m—Norwegian Sea
Dark grey mylonitic, granitic augen gneiss, with numerous thin (<1 mm) and some
thicker (<1 cm) leucocratic veins, concordant with the foliation in the rock.
Dispersed, oriented biotite and minor muscovite, along with stretched quartz and
feldspar, constitute the foliation. It is conceivable that some of the leucocratic bands
represent stretched out K-feldspar phenocrysts.
7128/4-1, 2527.0m—Finnmark Øst area, Barents Sea
Laminated shaly siltstone, with upward-fining layers of fine-grained sandstone (at
base) through siltstone to shale (at top). Some layers display erosional bases.
Although many primary sedimentary features are preserved in the rock, chlorite with
poorly-developed tails in the fine-grained layers suggest low-grade metamorphism
and a certain degree of deformation.
The appearance of this rock is similar to sandstones and shales of turbiditic origin in
the Kongsfjord Fm. or lower part of the overlying Båsnæringen Formation on the
Varanger Peninsula (A. Siedlecka, pers. com., 2006).
References
(Siedlecka 1972, Siedlecka and Edwards 1980, Pickering 1981, Siedlecka et al. 1995)
7128/4-1, 2527.2m—Finnmark Øst area, Barents Sea
Finely laminated siltstone, alternating with mm-thick upward-fining layers of sandy
siltstone. Locally the sandstone layers appear to have erosional bases, indicated by
what appears to be scour marks filled with relatively coarse sandstone.
The appearance of this rock is similar to sandstones and shales of turbiditic origin in
the Kongsfjord Fm. or lower part of the overlying Båsnæringen Formation on the
Varanger Peninsula (A. Siedlecka, pers. com., 2006).
References:
(Siedlecka 1972, Siedlecka and Edwards 1980, Pickering 1981, Siedlecka et al. 1995)
7128/4-1, 2528.1m—Finnmark East area, Barents Sea
Laminated fine-grained sandstone and shale, quite similar to 7128/4-1, 2527.2m, but
without the apparent sedimentary features.
The appearance of this rock is similar to sandstones and shales of turbiditic origin in
the Kongsfjord Fm. or lower part of the overlying Båsnæringen Formation on the
Varanger Peninsula (A. Siedlecka, pers. com., 2006).
References:
(Siedlecka 1972, Siedlecka and Edwards 1980, Pickering 1981, Siedlecka et al. 1995)
7128/6-1, 2540.5m—Finnmark Øst area, Finnmark Platform, Barents Sea
Fine-grained, layered metasandstone, with alternating layers of rusty brown sandstone
(0.5–1.5 cm thick) and grey sandstone (0.5–1 cm thick). The sandstone is
homogeneous and consists of ca. 0.5 mm poorly rounded quartz and feldspar grains in
a calcite-dominated matrix. The poor rounding and rather large amount of feldspar
indicate that the sediment was relatively immature. Røe and Roberts (1992) described
the sandstone in detail, and argued for lowermost greenschist-facies metamorphism
and postdepositional deformation.
7128/6-1, 2541.73m—Finnmark Øst area, Finnmark Platform, Barents Sea
Fine- to medium-grained, layered metasandstone, with alternating layers of rusty
brown sandstone (0.5–1.5 cm thick) and grey sandstone (0.5–1 cm thick).
7226/11-1, 5198.3m—Norsel High, Bjarmeland Platform, Barents Sea
Strongly foliated, medium-grained, biotite-rich schist (amphibolite?) with pods and
layers of quartz.
7226/11-1, 5198.8m—Norsel High, Bjarmeland Platform, Barents Sea
Strongly foliated, medium-grained, biotite-rich schist with pods and layers of quartz.
In addition to biotite, the matrix contains quartz, feldspar and some clinozoisite. The
rock also contains sulphides, most likely pyrite, aligned with the foliation.
References
Pickering, K.T. (1981) The Kongsfjord Formation - a Late Precambrian submarine
fan in north-east Finnmark, North Norway. Norges geologiske undersøkelse,
367, 77-104.
Røe, S.-L. and Roberts, D. (1992) Basement-core sandstones in well 7128/6-1,
southern Barents Sea, and correlation with onshore, Upper Proterozoic
sequences of northeastern Finnmark. Geological Institute, University of
Bergen, Unpublished report, 33 pp.
Siedlecka, A. (1972) Kongsfjord Formation-a Late Precambrian Flysch Sequence
form the Varanger Peninsula, Finnmark. Norges geologiske undersøkelse, 278,
41-80.
Siedlecka, A. and Edwards, M.B. (1980) Lithostratigraphy and sedimentation of the
Riphean Båsnæringen Formation, Varanger Peninsula, North Norway. Norges
geologiske undersøkelse, 355, 27-47.
Siedlecka, A., Negrutsa, V.Z. and Pickering, K.T. (1995) Upper Proterozoic Turbidite
System of the Rybachi Peninsula, northern Russia - a possible stratigraphic
counterpart of the Kongsfjord Submarine Fan of the Varanger Peninsula,
northern Norway. Norges geologiske undersøkelse Special Publication, 7,
201-216.