Tilje Formation (Tiljeformasjonen)
(From NPD Bulletin no. 4)
Båt Group
Name
The Norwegian word for a boat's decking. This unit corresponds to the
upper part of the informal Aldra formation (Hl-2).
Well type section
6507/11-1
(Saga Petroleum), coordinates 65°04'43.82"N, 07°29'23.33"E, from 2596 m to
2498 m (Fig. 9). Five cores (33 m recovery) were taken through the upper
part of the formation.
Well reference section
6609/10-1,
(Saga Petroleum), coordinates 66°14' 42.27"N, 09°14'59.50"E, from 1733 m
to 1642 m (Fig. 10). One core (11.5 m recovery) was taken uppermost in the
unit.
Thickness
98 m in the type well, 91 m in the reference well.
Lithology
Very fine to coarse-grained sandstones are in-terbedded with shales and
siltstones. The sandstones are commonly moderately sorted with a high clay
content and most beds are bioturbated. Shale clasts and coaly plant
remains are common. Pure shale beds are rare; most of the finer grained
interbeds are silty or sandy.
Basal Stratotype
The base of the Tilje Formation is defined at the top of a mudstone
interval recognized in most wells on Haltenbanken. The overlying sequence
shows a markedly higher sand content and a greater average thickness of
individual sandstone bodies. The gamma ray log shows a shift to generally
lower values and a slightly more blocky pattern over the boundary.
The mudstone interval is most pronounced on the Halten Terrace, but is
often difficult to pick further east on the Trøndelag Platform. Coal beds
are here developed at higher stratigraphic levels than on Halten Terrace,
and the top of the highest coal bed is recommended as the formational
boundary.
In the reference well from Trænabanken the formational base is taken at
an upward shift in the gamma ray log from relatively irregular, high
amplitude variations to more uniform, low amplitude and generally lower
readings. Limestone interbeds are common below the boundary and much less
frequent above in this area.
Lateral extent and variation
The formation is present both on Haltenbanken and Trænabanken, although
it is locally absent on the Nordland Ridge due to erosion. The formation
is uniformly developed throughout the Halten Terrace where it is from 100
m to 150 m thick, but it thins northeastwards to less than 100 m on the
Trøndelag Platform. Shallow drilling close to the coast (Bugge et al.
1984) indicates time equivalent deposits dominated by coarse-grained
elastics.
Age
Sinemurian to Pliensbachian.
Depositional environment
Nearshore marine to intertidal environments are typical of the formation.
Subcrops near the coast (Bugge et al. 1984) indicate a gradual transition
to continental environments eastwards.
Correlation
The Tilje Formation is comparable in age and lithology to the Neill
Klinter Formation of East Greenland and to the lower part of the Stø
Formation in the Hammerfest Basin.
