Ekofisk Formation CKEK

 

Premise Formation defined by van Adrichem Boogaert and Kouwe (1994). In the northern Netherlands offshore area an interval of Paleocene chalk is often found. In accordance with the lithostratigraphy in the adjoining offshore sectors of Denmark, Norway and the United Kingdom this interval has been split off from the Ommelanden Formation and placed in the Ekofisk Formation, which was defined by Deegan and Scull (1977) , with the type section in the Norwegian well 02/04-05, interval 3037-3164 m below.
  Paleocene chalk is also locally present in the southern North Sea area and in parts of the Netherlands onshore (Letsch and Sissingh (1983) ; Vinken (1988) ). Occurrences in the Roer Valley Graben and in the south of the province of Limburg have a different lithofacies, exhibiting coarser bioclastics. These have been assigned to the Houthem Formation
Derivatio nominis The name is commonly used for lithological equivalents in the Danish and Norwegian sectors, and part of the UK sector of the North Sea. Named after the Ekofisk Field in the Norwegian offshore block 2/4, which produces from the Chalk Group. The East Shetland Basin, a marl unit here assigned to the Maureen Formation rests directly on strata dated as Cretaceous. It is possible that condensed equivalents of the Ekofisk Formation are present at the base of this marl unit.
Type section Location map See figure (pdf)
  Well A12-01 (pdf)
  Location N 55°24'00.1
E 03°48'33.9
  Depth 2038 to 2123 m
  Length 85 m along hole
Additional section Location map See figure (pdf)
  Well B14-01 (pdf)
  Location N 55°12'16.9
E 04°34'35,5
  Depth 1898 to 1992 m
  Length 94 m along hole
Definition White, chalky limestones containing rare white and grey nodular and bedded chert layers, and thin, grey to green clay laminae. Some glauconite can occur in the basal interval. The unit displays a characteristic gradual increase in acoustic- and resistivity-log readings.
Upper Boundary The boundary with the overlying sands and clays of the Lower North Sea Group is expressed clearly on wire-line logs by the, for chalks, so characteristic pattern: a low gamma-ray response and a high acoustic velocity.
Lower Boundary The lower boundary with the Ommelanden Formation is characterised by a change to a slightly higher response and somewhat more serrate pattern of the gamma-ray curve, and a lower porosity in the basal Ekofisk Formation, as can be observed on the appropriate wire-line logs. In general, most of the formation shows a somewhat higher porosity than the uppermost Ommelanden Formation. Very rarely a high peak is seen on the gamma-ray log, representing a Cretaceous/Tertiary boundary clay layer, which equates the Fish Clay in Denmark Sorgenfrei (1957) . Locally, a densely cemented hardground level, overlain by a glauconite-rich bed, may occur around this boundary.
Correlation The Ekofisk Formation extends eastwards into Denmark, where it is represented onshore by the Danskekalk Formation. Although it probably extended over other parts of the Southern North Sea, it is now represented only by erosional remnants in Belgium (Mons Formation). The Ekofisk Formation has not been identified as such in the East Shetland Basin, although it is possibly represented in condensed form at the base of the marl unit here assigned to the Maureen Formation.
Distribution The formation occurs locally in the northern and southern Netherlands North Sea sector and parts of the onshore area (areas in the West Netherlands Basin and the Central Netherlands Basin).
Age Danian. Characteristic Foraminifera are Globorotalia compressa, Globigerina daubjergensis, Globigerina pseudobulloides (planktonic) and Gavelinella danica and Stensioeina beccariformis (benthic). The top of the formation is poorly characterized biostratigraphically, although there is a downhole decrease in the abundance and diversity of benthonic microfossils at this level. The S.inornata biomarker occurs within the formation.
Depositional Setting Similar to the Ommelanden Formation. In particular in the northern blocks A and B, where the formation may have been deposited in deeper water, redeposition by gravitational mass flow occurred. This is reflected in thin sections by a typical brecciated microstructure of the rocks.
References See References Upper Cretaceous

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