Ror Formation (Rorformasjonen)
(From NPD Bulletin no. 4)
Båt Group
Name
Norwegian word for rudder or helm. The previous informal unit was the Leka
formation (Hl-3).
Well type section
6407/2-1
(Saga Petroleum), coordinates 64°58'04.97"N, 07°28'28.11"E, from 3176 m to
3072 m (Fig. 13). One core (14.5 m recovery), from the upper parts of the
formation.
Well reference sections
6507/10-1
(BP), coordinates 65°13'10.75"N, 07°14'00.47"E from 3080.5 m to 2994 m
(Fig. 14). One core covers the base and 3.5 m of the lower part of the
unit.
6407/4-1
(Statoil), coordinates 64°35'45.36"N, 07°08'42.17"E,
from 4272 m to 4106 m (Fig. 12). The section includes approximately 40 m
of interbedded Tofte Formation.
6610/7-1
(Statoil), coordinates
66°17'32.82"N, 10°16'52.92"E, from 2745.5 m to 2679 m, (Fig. 15). Two
cores, 28 m recovery, cover both the middle and upper parts of the unit.
Thickness
104 m in the type well, from 66.5 m to 160.5 m
in the reference wells.
Lithology
Dominant grey to dark grey mudstones contain interbedded silty and sandy
coarsening upwards sequences, commonly a few metres thick. Such sequences
become more frequent towards the top of the formation, giving the unit an
overall coarsening upwards trend over most of Haltenbanken.
Basal Stratotype
The base is defined by the abrupt transition from sandstones of the
Tilje
Formation into mudstone. The break is well defined in most Haltenbanken
wells and is easily picked on the gamma log. Well correlation indicates an
ero-sional contact, at least in parts of the area.
In the northwesternmost Haltenbanken wells (e.g.
6506/12-1,
Fig. 11) the
Tofte Formation rests directly on the
Tilje Formation, with no
fine-grained succession in between. The mudstones overlying the Tofte
Formation there are equivalent to the upper part of the Ror Formation in
its type area.
Lateral extent and variation
The formation is present in all wells on Haltenbanken, where it varies
from 70 m to 170 m thick - generally thinning to the northeast. To the
west it interfingers with sandstones of the Tofte
Formation (Fig. 12), and
the oldest part of the Ror Formation is often absent. The Ror Formation is
also present in some Trænabanken wells (e.g. Fig. 15), but has been
removed by erosion over large areas of the Nordland Ridge.
Age
Pliensbachian to Toarcian.
Depositional environment
The formation was deposited in open shelf environments, mainly below wave
base. The coarsening upwards trend reflects ongoing shallowing and
storm-generated sands are common in the unit's upper part. Sand input from
the west indicates synsedimentary tectonic uplift along the western
margins of the basin.
