Rødby Formation (Rødbyformasjonen)
(From NPD Bulletin no. 5)
Cromer Knoll Group
Name
Named by Larsen (1966) after a town on the island of
Lolland in southern Denmark.
Well type section
The Danish well Rødby-1 drilled on the island of
Lolland (Larsen 1966).
Well reference sections
Norwegian well 2/11-1
from 2910 to 2887 m, coordinates N 56°14'16.98", E 03°27'07.05" (Fig. 12). No cores.
Norwegian well 2/7-15
from 3419 to 3401 m, coordinates N 56°23'46.82", E 03°18'54.63" (Fig. 22). No cores.
Thickness
In the well type section the thickness is 23 m. The thicknesses in the
reference sections are 23 m in well 2/11-1 and 18 m in well 2/7-15. The
formation generally ranges in thickness between 15 and 30 m. In the Viking Graben it may reach thicknesses of more than 200 m (Deegan & Scull 1977).
Lithology
Mainly red-brown marlstones, but green and grey colours may occur. Glauconite and pyrite may be present. Sandstones and siltstones are known to be present locally.
Basal stratotype
The lower boundary is placed on the Sola
and Åsgard Formations and the Ran
sandstone units, and represents an upward decrease in gamma-ray response
and usually an increase in velocity into the Rødby Formation
(Figs. 12,22 and 23).
Characteristics of the upper boundary
The upper boundary can be seen as an upward decrease in gamma-ray response
and a increase in velocity when going into the more calcareous sediments
of the Svarte Formation (Figs. 33-36). On the Horda
Platform the Rødby Formation is more calcareous and has a lower gamma-ray
response and a higher velocity than the overlying unspecified unit of the
Shetland Group (Fig. 37). Where the chalk facies
of the Shetland Group is present, the upper boundary is characterised by
a distinct upward drop in gamma-ray readings and a marked increase in
velocity (Figs. 12, 15, 22-28)1
Distribution
The formation is widespread in the North Sea, but are missing locally on the
Utsira, Jæren and Mandal Highs, Tampen Spur and Horda Platform on the
Norwegian sector.
Occurrences of formation tops in wells
Age
The formation is of Albian age (locally Early
Cenomanian in the Danish sector (Jensen et al. 1986)).
Depositional environment
The Rødby Formation was deposited as generally reddish sediments in an
open marine, oxygenated environment with limited supply of clastics.
