Garn Formation (Garnformasjonen)
(Modified from NPD Bulletin no. 4)
Fangst Group
Name
From the Norwegian word for a net. The unit corresponds to the upper part
of the Tomma formation (Hl-4) of informal usage, or "Tomma I".
Well type section
Well 6407/1-3
(Statoil), coordinates 64°52'25.48"N, 07°02'53.47"E, from 3704 m to 3600 m
(Fig. 20). The lower 84 m of the unit are cored, including the base.
Well reference section
Well 6507/11-3
(Saga Petroleum), coordinates 65°01'59.8"N, 07°30'42.34"E, from 2457 m to
2412 m (Fig. 16). The lower 29 m of the unit are cored, including the
base.
Thickness
104 m in the type well and 45 m in the reference well.
Lithology
The Garn Formation consists of medium to coarse-grained, moderately to
well-sorted sandstones. Mica-rich zones are present. The sandstone is
occasionally carbonate-cemented.
Basal Stratotype
The lower boundary is defined by a drop in gamma ray response from the underlying shaly
Not Formation into the Garn Fm. In the type
well this coincides with an erosional contact at the base of a thin
conglomerate.
In the western part of Haltenbanken a higher semi-regional gamma response in Garn sands can be wrongly
interpretated as the boundary with the Not Fm. These high gamma values are due
to local occurrence of radioactive heavy minerals in Garn sandstones. The type and reference wells of
the Garn Fm, further east on Haltenbanken do not display this radioactive anomaly.
Age
Bajocian to Bathonian.
Depositional environment
The Garn Formation may represent progradations of braided delta lobes.
Delta top and delta front facies with active fluvial and wave-influenced
processes are recognized.
Lateral extent and variation
The Garn Formation is encountered across most of Haltenbanken. It may be
over 100 m thick on the Halten Terrace, but in structurally high positions
the entire unit may be eroded. In the Trænabanken area shaly sediments
are lateral equivalents of the Garn Formation sandstones.
Correlation
The Garn Formation is time equivalent to parts of the
Brent Group in the
North Sea, to the lower part of the Vardekløft Formation in East Greenland
and to the upper part of the Stø Formation in the Hammerfest Basin.
Subdivision
The formation is not subdivided at present although two different units
may be identified in the western part of Haltenbanken.
