Åre Formation (Åreformasjonen)
(From NPD Bulletin no. 4)
Båt Group
Name
From the Norwegian word for oar. This formation corresponds to the
informal term Hitra formation ("the coal sequence" or Hl-1) together with
the lower part of the Aldra formation (Hl-2).
Well type section
6507/12-1
(Saga Petroleum), coordinates 65°07'01.62"N, 07°42'42.61"E from
2920 m to 2412 m (Fig. 7). Two cores, 26.2 m recovery.
Well reference section
6407/1-2
(Statoil), coordinates 64°47'50.61"N, 07°02'23.76"E, from 4548 m to
4221 m (Fig. 8). No cores.
Thickness
508 m in the type well. Generally between 300 m and 500 m.
Lithology
Alternating sandstones and claystones are in-terbedded with coals and
coaly claystones. The claystones are grayish or locally red brown and
noncalcareous to very calcareous. The sandstones are grayish, very fine to
coarse-grained and predominantly moderately to poorly sorted. The coals in
the type well are dark brown to black, vitreous, brittle and locally
pyritic.
Basal Stratotype
The base is defined directly underneath the lowermost coal bed identified
on the sonic log. In the type well the resistivity log increases slightly
and changes to a somewhat less nervous pattern at the transition into the
Åre Formation.
Lateral extent and variation
The formation is present in all areas drilled in the Haltenbanken -
Trænabanken region but seismic data indicate that it is truncated in
positive areas such as the Nordland Ridge. The upper part of the formation
contains a laterally continuous mudstone interval; this has a generally
uniform thickness, but thins slightly to the north.
Occurrences of formation tops in wells
Age
Rhaetian to Pliensbachian.
Depositional environment
Costal plain to delta plain deposits with swamps and channels pass upwards
into marginal marine facies. Individual coals can be up to 8 m thick. More
proximal lithofacies contain less coal and coarser sandstones. Shallow
drilling to the east shows conglomerates which are probably laterally
equivalent to the Åre Formation (Bugge et al. 1984).
Correlation
The formation is partially equivalent to the
Statfjord Formation in the
North Sea, to the combined upper Fruholmen, Tubåen and Nordmela formations
in the Hammerfest Basin and to the Kap Stewart Formation of eastern
Greenland. The Åre Formation has a lower sand content than the Statfjord
Formation in the northern North Sea.
