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
Cromer Knoll Group
The term Carrack Formation was first defined by Johnson & Lott (1993) in the Central North Sea area as a unit of dark grey, essentially non-calcareous, marine mudstones lying between the Valhall and Rødby formations. This unit replaces the Sola Formation of Andrews et al., (1990) and Gatliff et al. (1994). This unit has now been identified in the southern North Sea area (Lott & Knox, 1994), where it forms the poorly calcareous uppermost part of the Valhall Formation (Speeton Clay Formation as originally defined by Rhys, 1974).
From the large sailing merchant-ship, equipped for warfare.
In the Central and Northern North Sea the Carrack Formation comprises essentially non-calcareous, carbonaceous, pyritic, micaceous mudstones and siltstones with local sandstones (Johnson & Lott 1993). Mudstones are medium to dark grey and black (locally red-brown: e.g. Well 14/4-1), firm to hard and blocky to fissile, with some thin, greenish white tuffaceous layers (e.g. Well 15/21a-7 at 3142m; Well 14/20-8 at c. 2698 m). Thin beds of white to buff, microcrystalline, argillaceous limestones, dolomitic limestones and chalky mudstones are interbedded with the mudstones (e.g. Well 14/19-13). Local sandstones are fine- to coarse-grained and each sandstone unit usually displays upward fining. One of these sandstone units has been given member status (Skiff Sandstone Member).In the Southern North Sea, the Carrack Formation consists of poorly calcareous, occasionally sandy mudstones. The mudstones may be dark grey to red-brown or variegated (Lott & Knox, 1994). Thin sandy beds and phosphatic pebbles may also occur in the unit.
The Carrack Formation is generally between 40 and 100 m thick in the Central and Northern North Sea, although it is up to 200 m thick in the Moray Firth (Andrews et al., 1990). The formation thins or is absent over the Forties/Montrose high and Auk Platform areas (Johnson & Lott (1993); it is generally thin (<25 m) over much of the Southern North Sea area (Lott & Knox, 1994).
The Carrack Formation, though generally thin is present over much of the Southern North Sea area (Lott & Knox, 1994), Quadrants 35-39, 41-44, 47-49, 51-54. It is also widely distributed across the Central and Northern North Sea, Quadrants 6-9, 12-16, 19-23, 26-30. The formation may be absent over some intrabasinal highs, (e.g., Forties/Montrose High and Auk Platform) and its western limit is difficult to define on currently available well data (Johnson et al., 1993).
|Central North Sea (Johnson & Lott, 1993)|
15/16-14: 3094-3158 m (10151-10361 ft)
|Lat. 58º 22’ 11.4”N
Lat. 57º 47’ 59.7”N
Lat. 56º 49’ 51.95”N
|Long. 00º 04’ 25.3”E
Long. 00º 29’ 28.0”W
Long.01º 43’ 20.37”E
|Southern North Sea (Lott & Knox, 1994)|
|44/24-1: 13931402 m (45704600 ft)
47/9b-6: 666680 m (21852231 ft)
48/22-3: 420.5430 m (13801411 ft)
49/25a-5: 18121853 m (59456080 ft)
|Lat. 54º 15’09.8”N
Lat. 53º 45’ 24.687”N
Lat. 53º17’ 31.3”N
Lat. 53º 13’ 34.6”N
|Long. 02º 40’46.22E
Long. 00º 42’ 16.713”E
Long. 01º 15’ 58.9”E
Long. 02º 49’ 39.7”E
The top of the formation is normally marked by a downward change from pale to dark grey and red brown calcareous mudstones, chalky mudstones and thin, interbedded limestones (Rødby Formation) to dark grey and black, non-calcareous (or poorly calcareous in the Southern North Sea) mudstones. It is marked by a downward increase in gamma-ray values and a downward decrease in velocity and density (Lott & Knox, 1994).Where the Rødby Formation is absent, the Chalk Group rests unconformably on the Carrack Formation.
Central and Northern North Sea (Johnson & Lott, 1993): The base is normally taken at the downward change from dark grey-black, non-calcareous and carbonaceous mudstone (Carrack Formation) to chestnut brown, brick red, reddish grey or pale calcareous mudstones and chalky mudstones (Valhall Formation). It is marked on wireline logs by a sharp downward increase in velocity and density. Locally in the Central and Northern North Sea the formation rests on the Wick Sandstone and Britannia Sandstone formations.Southern North Sea (Lott & Knox, 1994): The base of the Carrack Formation is normally characterized by a sharp downward change from dark, poorly calcareous mudstones to a paler, harder chalky mudstone development at the top of the underlying Valhall Formation. There is a corresponding decrease in gamma values and marked increase in velocity.
The top of the Carrack Formation is dominated by calcareous benthonic foraminifera characteristic of the Globigerinelloides gyroidinaeformis biomarker, although the biomarker itself is in the very basal part of the overlying formation, immediately above the Rødby/Carrack formational boundary. Agglutinated foraminifera are characteristic of the middle part of the formation and the Verneuilinoides chapmani biomarker is recognized by the influx of a diverse agglutinated assemblage. Near the base of the formation, the Gaudryina dividens biomarker, with calcareous benthonic foraminifera and the ostracod Saxocythere tricostata have been recorded (e.g. Lott et al., 1985). The Micrantholithus hoschulzii / Micrantholithus obtusus and Rhagodiscus asper acme nannofossil biomarkers have been noted in the Carrack Formation. Dinoflagellate cyst floras from the Carrack Formation are abundant and diverse; the Subtilisphaera perlucida and Cerbia tabulata biomarkers occur within this formation.
The Carrack Formation passes laterally westwards into the upper part of the Speeton Clay Formation of the Cleveland Basin. The formation equates in part with the A-beds of the Speeton Clay and further south with the Carstone Formation and Sutterby Marl.
The poorly calcareous marine mudstones of the Carrack Formation contain a moderately rich microfauna including benthonic foraminifera but dominated by agglutinating species such as Glomospira and Recurvoides (Crittenden, 1987b) suggesting a phase of basin restriction and bottom-water oxygen depletion. Mudstones with abundant planktonic foraminifera may represent transgressive pulses (Andrews et al., 1990).
The Carrack Formation has the formal subdivision into the late Aptian Skiff Sandstone Member. It comprises fine- to coarse-grained mass-flow sandstone units, commonly displaying upward-fining, located in the South Viking Graben (Johnson & Lott, 1993).