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
The term Flounder Formation was introduced by Deegan & Scull (1977) for a unit of mudstones and interbedded limestones that lay between the Herring Formation and the Tor Formation (Table 1). This definition was adopted by Johnson & Lott (1993) except that, in contrast to Deegan & Scull (1977), the Flounder Formation is included in the Shetland Group.
From the salt-water flat-fish.
The Flounder Formation is up to 500 m in thickness in the Fisher Bank Basin, but is absent over the crest of the Forties-Montrose High (Gatliff et al., 1994). Seismic evidence suggests that it broadly onlaps, and becomes very thin over, contemporary structural highs (Gatliff et al., 1994). Andrews et al. (1990) interpreted a significant unconformity or hiatus within the Flounder Formation.
The Flounder Formation is confined to the southern part of the South Viking Graben and the extreme north of the Central North Sea.
16/17-6: 3249-3590.5 m(10660-11779 ft)
|Lat. 58°25’ 55.6”N||Long. 01°18’ 26.0”E|
The top of the Flounder Formation is normally marked by a relatively abrupt downward change from the hard chalky limestones of the Tor Formation to calcareous mudstones with interbedded argillaceous chalky limestones, which are commonly stained pink or red.
The top of the Flounder Formation is marked by the Reussella szajnochae acme foraminiferal biomarker, which in the Central North Sea is accompanied by the FDO of Tritaxia capitosa. In some areas, this biomarker occurs at the top of the formation; in others it is just below the top (this is also implied in King et al., 1989, fig.8.4). Long-ranging planktonic foraminifera, particularly species of Rugoglobigerina, are common. The Cenosphaera sp. radiolarian biomarker is present in the middle part of the formation. The Stensioeina granulata polonica and S. granulata granulata biomarkers also occur within the formation.
Three key calcareous nannofossil biomarkers occur: the Reinhardtites anthophorus biomarker, at the top of the formation, the Broinsonia enormis biomarker, at the top of the early Santonian, and Watznaueria barnesae acme biomarker, which marks the mid/early Santonian boundary, in the middle part of the formation. The Helicolithus trabeculatus biomarker and H. valhallensis acme biomarker also occur within the formation.
In the Central North Sea, the Flounder Formation grades laterally into the Mackerel Formation. In the South Viking Graben, the Flounder Formation passes northwards into the Kyrre Formation and the lower part of the Jorsalfare Formation (J1 and the basal part of J2) (see Panel 3 of Johnson & Lott, 1993). Red coloration in the unit of interbedded argillaceous chalky limestone and mudstone near the top of the formation in well 22/l -2A supports a wireline-log correlation with the characteristically red, calcareous unit (J1) at the base of the Jorsalfare Formation.
The Flounder Formation comprises marine hemipelagic mudstones and pelagic limestones that accumulated in low-energy shelf to upper bathyal conditions. Phases of more open marine circulation are indicated by a higher proportion of planktonic foraminifera in the Coniacian and Upper Campanian (King et al., 1989).
King et al. (1989) informally divided the Flounder Formation into three units of pale grey mudstone with argillaceous limestone, and three intervening units of red-stained, and generally more argillaceous mudstone. On the basis of wireline-log signatures, Andrews et al. (1991) recognized four chalk-marl cycles, each up to about 100 m thick in the Flounder Formation of the Moray Firth and subdivided it into four informal units (designated F1 to F4). The Flounder Formation was not formally subdivided by Johnson & Lott (1993), although informal subdivisions are recognized and correlated locally.