updated to follow: Stratigraphic Guide to the Cromer Knoll, Shetland and Chalk Groups of the North Sea and Norwegian Sea. Felix M. Gradstein & Colin C. Waters (editors), Mike Charnock, Dirk Munsterman, Michelle Hollerbach, Harald Brunstad, Øyvind Hammer & Luis Vergara (contributors). Newsletter on Stratigraphy, vol 49/1 pp71-280, 2016(From NPD Bulletin no. 5)
Cromer Knoll Group
The definition of the Rødby Formation follows that described in Isaksen & Tonstad (1989) for the Norwegian Sector. In the UK Sector the definition is set out by Johnson & Lott (1993) for the Central and Northern North Sea, which follows that of Larsen (1966) and Deegan & Scull (1977). Because of the ease with which this unit may be correlated into the Southern North Sea Basin, the usage of the term Rødby Formation was extended by Lott & Knox (1994) and replaces the term Red Chalk Formation formerly used for this unit by Rhys (1974). The Rødby Formation generally forms the topmost unit of the Cromer Knoll Group.
From the town of Rødby on the island of Lolland in southern Denmark (Larsen, 1966).
Norway Central Graben and Viking Graben (Isaksen &&Tonstad 1989): 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.
UK Central to Northern North Sea (Johnson & Lott, 1993): Mudstones (calcareous and chalky) with sporadic thin beds of argillaceous limestone. Mudstones are soft to hard, blocky to fissile, micaceous, glauconitic and sometimes silty. They are mainly pale to dark grey, but often red-brown, brick red, olive grey and dark brown. The red coloration is more often developed in the lower and upper parts of the formation and used for informal subdivision. The interbedded limestones are white to pale grey, tan and re-brown to pink, firm, argillaceous and microcrystalline.
UK Southern North Sea (Lott & Knox, 1994): Calcareous mudstones, chalky mudstones and chalky limestones. They range in colour from pink, pale red, red-brown to brown-grey and often show a variegated, colour-mottled appearance. The mudstones are firm to hard and become increasingly calcareous upwards before passing into the overlying pelagic white to pale grey chalks of the Chalk Group.
In the well type section in the Danish Sector, the thickness is 23 m.
Norway Central Graben and Viking Graben (Isaksen & Tonstad, 1989): 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 become 200 m or more thick (Deegan & Scull, 1977).
UK Sector : The Rødby Formation is generally about 80-180 m thick in the Outer Moray Firth, up to about 90 m thick over the Halibut Shelf (e.g. 13/14-1) and up to about 100 m in the South Viking Graben (e.g. 16/12b-6) and Central Graben (Johnson & Lott, 1993). In the Northern North Sea the formation is typically only a few metres thick (e.g., 211/27-10 comprises 8 m of reddish brown to pale green or grey claystone, calcareous claystone and limestone (Johnson et al., 1993). However, in the Magnus Trough, an exceptionally thick development, 731 m thick, is recorded in well 210/15-4 (Johnson et al., 1993). In the Southern North Sea the formation is generally between 20 and 30 m in thickness but exceptionally may reach 50 m in thickness (e.g. 53/4-6, Lott & Knox, 1994).
The Rødby Formation is widely correlatable throughout much of the North Sea Basin. However, it is locally absent on the Utsira-, Jæren-, and Mandal Highs, Tampen Spur and Horda Platform. Formation tops in wells may be obtained from a routine on the Norlex website under this formation.In the UK Sector it is present in the Central North Sea, South Viking Graben, Moray Firth, Central Graben, Southern North Sea (as far south as approx. 52 degrees 30 minutes N) and off the coast of Yorkshire, Lincolnshire and Norfolk. In the Southern North Sea the Rødby Formation occurs throughout the basinal areas but may be absent over some intra-basinal highs (e.g. 53/2-5, Panel 1, Lott & Knox, 1994).
Interval of type section & thickness in type well: 459469 m (15061539 ft) below ground level (Larsen, 1966).
Norwegian well 2/11-1from 2910 to 2887 m, coordinates N 56°14'16.98", E 03°27'07.05" (Figure 12 in Isaksen & Tonstad (1989)). No cores. Norwegian well 2/7-15 from 3419 to 3401 m, coordinates N 56°23'46.82", E 03°18'54.63" (Figure 22 in Isaksen & Tonstad (1989)). No cores.
|Central and Northern North Sea (Johnson & Lott, 1993)|
14/4-1: 1219-1279 m (3999-4196 ft)
|Lat. 58º 59’ 52”N
Lat. 58º 24’ 41.3”N
Lat. 58º 37’ 23.076”N
Lat. 56º 51’ 25.18”N
| Long. 00º 23’ 44”W
Long. 00º 06’ 20.9”W
Long. 01º 20’ 57.813”E
Long. 01º 17’ 59.64”E
|Southern North Sea (Lott & Knox, 1994)|
|44/24-1: 13651393 m (44784570 ft)
48/22-3: 397.5420.5 m (13041380 ft)
49/24-1: 1292.51325 m (42404347 ft) **
53/4-6: 11841236 m (38864055 ft)
|Lat. 54º 15’ 0.98”N
Lat. 53º17’ 31.3”N
Lat. 53º 16’ 49.5”N
Lat. 52є 59’ 06.71”N
| Long. 02º 40’ 46.2”E
Long. 01º 15’ 58.9”E
Long. 02º 41’ 30.4”E
Long. 02º 44’ 11.75”E
** type section for Red Chalk Formation of Rhys (1974); see Crittenden (1984) for description of the foraminifera present in this well.
Norwegian Sector: The upper boundary can be seen as an upward decrease in gamma-ray response, and an increase in velocity into the more calcareous sediments of the Svarte Formation (Figures 33-36 in Isaksen &&Tonstad (1989)). On the Horda Platform the Rødby Formation is more calcareous; it also has a lower gamma-ray response, and a higher velocity than the overlying unspecified unit of the Shetland Group (Figure 37 in Isaksen & Tonstad (1989)). 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 (Figures 12, 15 and 22-28 in Isaksen & Tonstad (1989)).UK Sector: In the Central and Northern North Sea there is a subtle downward change from interbedded pale to dark grey and pink limestones, argillaceous chalks and calcareous mudstones (Hidra Formation, Chalk Group) to less calcareous mudstones and chalky mudstones with interbedded limestones (Rødby Formation). In the Southern North Sea the boundary is less subtle and corresponds to the change from grey and white chalk (Hidra Formation) to red-brown chalky mudstones (Rødby Formation). The upper boundary of the formation corresponds to a moderately sharp downward increase in gamma-ray values and a downward decrease in sonic velocity (Johnson & Lott, 1993; Lott & Knox, 1994).
Norwegian Sector: The lower boundary is placed on the Sola and Åsgard Formations and on the Ran Member; it represents an upward decrease in gamma-ray response and usually an increase in velocity into the Rødby Formation (Figures 12, 22 and 23 in Isaksen & Tonstad (1989)).
UK Sector: In the Central to Northern North Sea, the base of the Rødby Formation is taken at a transitional downward change from grey and red brown chalky mudstones and calcareous mudstones with interbedded limestones to dark grey, non-calcareous mudstones of the Carrack Formation (Johnson & Lott, 1993). Locally, where the basal beds are absent, the boundary is sharp (e.g. Well 16/12b-6 in the southern Viking Graben) and in some areas of the Inner Moray Firth the boundary is a downward change to sandstone (Wick Sandstone Formation).
In the Southern North Sea, the base of the Rødby Formation is taken at a change from reddened mudstones and chalky limestones to the mudstones of the Carrack Formation. In some wells sited over structural highs the formation may rest directly on thin sandy sediments of Jurassic or older strata. (e.g., 49/9-1, Lott & Knox, 1994).
In the UK Sector long-ranging planktonic foraminifera, particularly species of Hedbergella, are abundant in the Rødby Formation, accompanied by the Osangularia schloenbachi biomarker. The top of the formation is characterized by the FDO of Arenobulimina chapmani and the ostracod Isocythereis fissicostis. The following microfaunal biomarkers can be recognised within the formation: the Globigerinelloides bentonensis biomarker, the Neocythere ventrocostata biomarker and the Arenobulimina macfadyeni biomarker. The Globigerinelloides gyroidinaeformis biomarker, is at the base of the Rødby Formation (Crittenden et al., 1991). Two calcareous nannofossil biomarkers are recognised in the middle of the Rødby Formation, based on the FDOs of Hemipodorhabdus gorkae and Gartnerago praeobliquum.
The dinoflagellate cyst floras of the Rødby Formation are diverse and generally well preserved (Crittenden et al., 1991), and by analogy with the Central North Sea and onshore areas, the Ovoidinium scabrosum and Apteodinium maculatum subsp. grande biomarkers occur at the top of the formation and Protoellipsodinium spinosum and Systematophora cretacea in the middle of the unit.
In eastern England in the onshore succession of East Anglia, the Rødby Formation equates for the most part with the Hunstanton Formation (formerly the Red Chalk) (Rawson, 1992).
The Rødby Formation is a highly condensed sequence of sediments which were deposited in a well-oxygenated shallow-marine environment with limited supply of clastics and which have a rich faunal assemblage. The microfauna in Unit R2 is dominated by agglutinating foraminifera indicating a phase of more restricted water circulation (Johnson & Lott, 1993). The formation marks a transitional phase of sedimentation between the hemipelagic mudstone dominated lithologies of the underlying early Cretaceous into the pelagic chalk-dominated lithologies of the overlying late Cretaceous. The characteristic red to red-brown coloration of much of the formation has been attributed to a variety of processes ranging from weathering of reddened lateritic soils to diagenetic changes (e.g. Jeans, 1980).
The Rødby Formation in the Central and Northern North Sea is commonly divisible into three informal units R1 to R3 upwards (Johnson & Lott, 1993). In some wells within the Southern North Sea Basin (e.g. 53/4-6) these three divisions can be recognized but in the majority where the sequence is commonly much thinner and more condensed, only the basal R1 unit may be apparent (e.g. 49/24-1, Lott & Knox, 1994). Consequently the application of these subdivisions is not considered to be appropriate at present for most wells the Southern North Sea area.