Coevorden Formation SKCF

 

Premise Definition extended after NAM and RGD (1980) .
Derivatio nominis Named after the town of Coevorden in the southeastern part of the Dutch province of Drente.
Type section Location map See figure (pdf)
  Well Schoonebeek-197 (pdf)
  Location N 52°38’58.0
E 07°02’34.2
  Depth 944 to 1230 m
  Length 286 m along hole
  Reference NAM and RGD (1980)
Additional section Location map See figure (pdf)
  Well Ruinen-1 (pdf)
  Location N 52°44’09.8
E 06°27’12.8
  Depth 994 to 1046 m
  Length 52 m along hole
  Well Exloo Odoorn-2 (pdf)
  Location N 52°54’20.7
E 06°51’57.8
  Depth 1644 to 1697 m
  Length 53 m along hole
  Well De Bente-1 (pdf)
  Location N 52°41’37.8
E 06°46’15.7
  Depth 1109.5 to 1174 m
  Length 64.5 m along hole
  Well Oldenzaal-2 (pdf)
  Location N 52°17’18.8
E 06°56’23.8
  Depth 114.2 to 295 m
  Length 180.8 m along hole
Definition Sequence of brownish-grey, marly, rarely sandy, clay-stones with occasional limestone beds, notably in its basal part. Thelimestone beds consist of pelecypod (typically Neomiodon; syn.: Cyrena) and/or ostracod microcoquina laminae. Claystones are usually finely laminated. In outcrops the cone-in-cone structure (Ger.: ’T├╝tenkalk’) is characteristic. On salt-domes (e.g. well Exloo Odoorn-2) and basin fringe settings, limestone beds are common throughout the formation.
Upper Boundary The Coevorden formation lies below the basal, generally glauconitic beds of the Rijnland Group (NAM and RGD (1980) ).
Lower Boundary The formation is located on top of the claystone-marl-evaporite succession of the Weiteveen Formation. In some halokinetically influenced settings the Weiteveen Formation can be absent. There the Coevorden immediately and unconformably overlies the Altena Group or older deposits. The contact with the Weiteveen Formation (Serpulite Member) is marked by a clear claystone break, which is seen prominently on resistivity and sonic logs.
Distribution Dutch part of the Lower Saxony Basin, which covers the easternmost parts of the provinces of Groningen, Drente and Overijssel. In the German part of the Lower Saxony Basin referred to as Wealden or B├╝ckeberg Formation
Age Ryazanian - earliest Valanginian(?). A well-established re-gional zonation exists (Wealden 1-6), on the basis of fresh-water ostracod associations found in German sections (Wolburg (1949) ; Sung (1955) ). The Ryazanian is characterised by Cicatricosisporites-Plicatella-dominated sporomorph assemblages Herngreen et al (1980) .
Depositional Setting Lithofacies associations and palaeontological data indicate a fresh- to brackish-water lake-basin to marginal-marine sub-basin (lagoon) setting. Lithofacies change laterally, but the associations can be grouped into palaeogeographically controlled facies-belts (Schott (1951) ; t Hart (1969) . Fine clastics dominate the basinal areas, while carbonates (shell beds) prevail in the basin-fringe and isolated elevated areas (e.g. salt-domes). These end-members are separated by a wide belt of transitional facies. The true basinal development is only known in the Netherlands from type well Schoonebeek-197.
Sequence Stratigraphy The formation represents sequences LZB 1.5b and LZB 1.6. The youngest occurrences of the Upper Coevorden Member might even belong to LZB 2.1.
Subdivision  
  In the type area the formation is subdivided into three members:
  SK Niedersachsen Group
  SKCF Coevorden Formation
  SKCFU Upper Coevorden Member
  SKCFM Middle Coevorden Member
  SKCFL Lower Coevorden Member
  This subdivision can be traced across the entire Dutch part of the Lower Saxony Basin. An informal use of the subdivision would be preferred in more remote areas.
References See References Upper Jurassic/ Lower Cretaceous

Van Adrichem Boogaert, H.A. & Kouwe, W.F.P., 1993-1997. [Stratigraphic unit]. In: Stratigraphic Nomenclature of the Netherlands.
Retrieved [Datum] from [url].